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https://github.com/tstack/lnav
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472 lines
12 KiB
C++
472 lines
12 KiB
C++
/*
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K-Way Merge Template
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By Jordan Zimmerman
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*/
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#ifndef KMERGE_TREE_H
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#define KMERGE_TREE_H
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/*
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K-Way Merge
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An implementation of "k-Way Merging" as described in "Fundamentals of Data Structures" by Horowitz/Sahni.
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The idea is to merge k sorted arrays limiting the number of comparisons. A tree is built containing the
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results of comparing the heads of each array. The top most node is always the smallest entry. Then, its
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corresponding leaf in the tree is refilled and the tree is processed again. It's easier to see in the
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following example:
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Imagine 4 sorted arrays:
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{5, 10, 15, 20}
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{10, 13, 16, 19}
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{2, 19, 26, 40}
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{18, 22, 23, 24}
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The initial tree looks like this:
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2
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/ \
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2 5
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/ \ / \
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18 2 10 5
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The '/' and '\' represent links. The bottom row has the leaves and they contain the heads of the arrays.
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The rows above the leaves represent the smaller of the two child nodes. Thus, the top node is the smallest.
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To process the next iteration, the top node gets popped and its leaf gets refilled. Then, the new leaf's
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associated nodes are processed. So, after the 2 is taken, it is filled with 19 (the next head of its array).
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After processing, the tree looks like this:
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5
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/ \
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18 5
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/ \ / \
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18 19 10 5
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So, you can see how the number of comparisons is reduced.
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A good use of this is when you have a very large array that needs to be sorted. Break it up into n small
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arrays and sort those. Then use this merge sort for the final sort. This can also be done with files. If
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you have n sorted files, you can merge them into one sorted file. K Way Merging works best when comparing
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is somewhat expensive.
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*/
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#include <math.h>
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#include <functional>
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template <class T, class owner_t, class iterator_t, class comparitor = std::less<T> >
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class kmerge_tree_c
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{
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public:
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// create the tree with the given number of buckets. Call add() for each of the buckets
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// and then call execute() to build things. Call get_top() then next() until get_top returns
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// false.
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kmerge_tree_c(long bucket_qty);
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~kmerge_tree_c();
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// add a sorted collection to the tree
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//
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// begin/end - start end of a collection
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void add(owner_t *owner, iterator_t begin, iterator_t end);
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// process the first sort
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void execute(void);
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// advance to the next entry
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void next(void);
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// return the next entry without re-processing the tree
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// if false is returned, the merge is complete
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bool get_top(owner_t *&owner, iterator_t& iterator)
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{
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if (top_node_ptr_mbr->has_iterator) {
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owner = top_node_ptr_mbr->owner_ptr;
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iterator = top_node_ptr_mbr->current_iterator;
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return iterator != top_node_ptr_mbr->end_iterator;
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}
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else {
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return false;
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}
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}
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private:
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class node_rec
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{
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public:
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node_rec(void) :
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left_child_ptr(NULL),
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right_child_ptr(NULL),
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parent_ptr(NULL),
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next_ptr(NULL),
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previous_ptr(NULL),
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next_leaf_ptr(NULL),
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source_node_ptr(NULL),
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owner_ptr(NULL),
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has_iterator(false)
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{
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}
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~node_rec()
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{
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delete left_child_ptr;
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delete right_child_ptr;
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}
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node_rec* left_child_ptr; // owned the left child of this node
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node_rec* right_child_ptr; // owned the right child of this node
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node_rec* parent_ptr; // copy the parent of this node
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node_rec* next_ptr; // copy the next sibling
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node_rec* previous_ptr; // copy the previous sibling
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node_rec* next_leaf_ptr; // copy only for the bottom rows, a linked list of the buckets
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node_rec* source_node_ptr; // copy ptr back to the node from whence this iterator came
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owner_t *owner_ptr;
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int has_iterator;
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iterator_t current_iterator;
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iterator_t end_iterator;
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private:
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node_rec(const node_rec&);
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node_rec& operator=(const node_rec&);
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};
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void build_tree(void);
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node_rec* build_levels(long number_of_levels);
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void build_left_siblings(kmerge_tree_c::node_rec* node_ptr);
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void build_right_siblings(kmerge_tree_c::node_rec* node_ptr);
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void compare_nodes(kmerge_tree_c::node_rec* node_ptr);
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comparitor comparitor_mbr;
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long bucket_qty_mbr;
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long number_of_levels_mbr;
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node_rec* top_node_ptr_mbr; // owned
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node_rec* first_leaf_ptr; // copy
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node_rec* last_leaf_ptr; // copy
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};
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inline long kmerge_tree_brute_log2(long value)
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{
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long square = 2;
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long count = 1;
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while ( square < value )
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{
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square *= 2;
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++count;
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}
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return count;
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} // kmerge_tree_brute_log2
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//~~~~~~~~~~class kmerge_tree_c
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template <class T, class owner_t, class iterator_t, class comparitor>
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kmerge_tree_c<T, owner_t, iterator_t, comparitor>::kmerge_tree_c(long bucket_qty) :
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bucket_qty_mbr(bucket_qty),
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number_of_levels_mbr(bucket_qty ? ::kmerge_tree_brute_log2(bucket_qty_mbr) : 0), // don't add one - build_levels is zero based
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top_node_ptr_mbr(NULL),
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first_leaf_ptr(NULL),
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last_leaf_ptr(NULL)
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{
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build_tree();
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}
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template <class T, class owner_t, class iterator_t, class comparitor>
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kmerge_tree_c<T, owner_t, iterator_t, comparitor>::~kmerge_tree_c()
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{
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delete top_node_ptr_mbr;
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}
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/*
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Unlike the book, I'm going to make my life easy
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by maintaining every possible link to each node that I might need
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*/
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template <class T, class owner_t, class iterator_t, class comparitor>
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void kmerge_tree_c<T, owner_t, iterator_t, comparitor>::build_tree(void)
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{
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// the book says that the number of levels is (log2 * k) + 1
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top_node_ptr_mbr = build_levels(number_of_levels_mbr);
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if ( top_node_ptr_mbr )
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{
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build_left_siblings(top_node_ptr_mbr);
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build_right_siblings(top_node_ptr_mbr);
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}
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}
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/*
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highly recursive tree builder
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as long as number_of_levels isn't zero, each node builds its own children
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and updates the parent link for them.
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If no children are to be built (i.e. number_of_levels is 0), then the leaf linked list is created
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*/
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template <class T, class owner_t, class iterator_t, class comparitor>
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typename kmerge_tree_c<T, owner_t, iterator_t, comparitor>::node_rec *
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kmerge_tree_c<T, owner_t, iterator_t, comparitor>::build_levels(long number_of_levels)
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{
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node_rec* node_ptr = new node_rec;
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if ( number_of_levels )
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{
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node_ptr->left_child_ptr = build_levels(number_of_levels - 1);
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if ( node_ptr->left_child_ptr )
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{
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node_ptr->left_child_ptr->parent_ptr = node_ptr;
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node_ptr->right_child_ptr = build_levels(number_of_levels - 1);
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if ( node_ptr->right_child_ptr )
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{
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node_ptr->right_child_ptr->parent_ptr = node_ptr;
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}
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}
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}
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else
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{
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if ( last_leaf_ptr )
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{
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last_leaf_ptr->next_leaf_ptr = node_ptr;
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last_leaf_ptr = node_ptr;
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}
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else
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{
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first_leaf_ptr = last_leaf_ptr = node_ptr;
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}
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}
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return node_ptr;
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}
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/*
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when we process a comparison, we'll have to compare two siblings
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this code matches each link with its sibling
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To get every node correct, I had to write two routines: one which works
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with left nodes and one which works with right nodes. build_tree() starts it
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off with the top node's children and then these two swing back and forth
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between each other.
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*/
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template <class T, class owner_t, class iterator_t, class comparitor>
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void kmerge_tree_c<T, owner_t, iterator_t, comparitor>::build_left_siblings(kmerge_tree_c<T, owner_t, iterator_t, comparitor>::node_rec* node_ptr)
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{
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if ( node_ptr->parent_ptr )
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{
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if ( node_ptr->parent_ptr->right_child_ptr )
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{
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node_ptr->next_ptr = node_ptr->parent_ptr->right_child_ptr;
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node_ptr->parent_ptr->right_child_ptr->previous_ptr = node_ptr;
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}
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}
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if ( node_ptr->left_child_ptr )
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{
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build_left_siblings(node_ptr->left_child_ptr);
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}
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if ( node_ptr->right_child_ptr )
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{
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build_right_siblings(node_ptr->right_child_ptr);
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}
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}
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template <class T, class owner_t, class iterator_t, class comparitor>
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void kmerge_tree_c<T, owner_t, iterator_t, comparitor>::build_right_siblings(kmerge_tree_c<T, owner_t, iterator_t, comparitor>::node_rec* node_ptr)
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{
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if ( node_ptr->parent_ptr )
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{
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if ( node_ptr->parent_ptr->left_child_ptr )
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{
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node_ptr->previous_ptr = node_ptr->parent_ptr->left_child_ptr;
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node_ptr->parent_ptr->left_child_ptr->next_ptr = node_ptr;
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}
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}
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if ( node_ptr->right_child_ptr )
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{
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build_right_siblings(node_ptr->right_child_ptr);
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}
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if ( node_ptr->left_child_ptr )
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{
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build_left_siblings(node_ptr->left_child_ptr);
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}
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}
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// fill the leaf linked list
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template <class T, class owner_t, class iterator_t, class comparitor>
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void kmerge_tree_c<T, owner_t, iterator_t, comparitor>::add(owner_t *owner, iterator_t begin, iterator_t end)
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{
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if ( begin == end )
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{
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return;
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}
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node_rec* node_ptr = first_leaf_ptr;
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while ( node_ptr )
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{
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if ( node_ptr->has_iterator )
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{
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node_ptr = node_ptr->next_leaf_ptr;
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}
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else
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{
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node_ptr->has_iterator = true;
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node_ptr->owner_ptr = owner;
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node_ptr->current_iterator = begin;
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node_ptr->end_iterator = end;
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break;
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}
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}
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}
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/*
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fill the initial tree by comparing each sibling in the
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leaf linked list and then factoring that up to the parents
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This is only done once so it doesn't have to be that efficient
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*/
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template <class T, class owner_t, class iterator_t, class comparitor>
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void kmerge_tree_c<T, owner_t, iterator_t, comparitor>::execute(void)
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{
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for ( long parent_level = 0; parent_level < number_of_levels_mbr; ++parent_level )
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{
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// the number of nodes to skip is (parent level + 1) ^ 2 - 1
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long skip_nodes = 2;
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for ( long skip = 0; skip < parent_level; ++skip )
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{
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skip_nodes *= 2;
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}
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--skip_nodes;
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node_rec* node_ptr = first_leaf_ptr;
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while ( node_ptr )
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{
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node_rec* parent_ptr = node_ptr;
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long i;
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for ( i = 0; i < parent_level; ++i )
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{
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parent_ptr = parent_ptr->parent_ptr;
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}
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compare_nodes(parent_ptr);
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for ( i = 0; i < skip_nodes; ++i )
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{
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node_ptr = node_ptr->next_leaf_ptr;
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}
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node_ptr = node_ptr->next_leaf_ptr;
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}
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}
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}
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// compare the given node and its sibling and bubble the result up to the parent
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template <class T, class owner_t, class iterator_t, class comparitor>
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void kmerge_tree_c<T, owner_t, iterator_t, comparitor>::compare_nodes(kmerge_tree_c<T, owner_t, iterator_t, comparitor>::node_rec* node_ptr)
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{
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// assert(node_ptr->parent_ptr);
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node_rec* node1_ptr = NULL;
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node_rec* node2_ptr = NULL;
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if ( node_ptr->next_ptr )
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{
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node1_ptr = node_ptr;
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node2_ptr = node_ptr->next_ptr;
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}
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else
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{
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node1_ptr = node_ptr->previous_ptr;
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node2_ptr = node_ptr;
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}
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long result;
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if ( !node2_ptr->has_iterator ) {
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result = -1;
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}
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else if ( !node1_ptr->has_iterator) {
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result = 1;
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}
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else if ( (node1_ptr->current_iterator != node1_ptr->end_iterator) && (node2_ptr->current_iterator != node2_ptr->end_iterator) )
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{
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// no need to check for exact equality - we just want the lesser of the two
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result = comparitor_mbr(*node1_ptr->current_iterator, *node2_ptr->current_iterator) ? -1 : 1;
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}
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else if ( node1_ptr->current_iterator != node1_ptr->end_iterator )
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{
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result = -1;
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}
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else // if ( node2_ptr->current_iterator != node2_ptr->end_iterator )
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{
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result = 1;
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}
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node_rec* winner_ptr = (result <= 0) ? node1_ptr : node2_ptr;
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node_rec* parent_ptr = node_ptr->parent_ptr;
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parent_ptr->owner_ptr = winner_ptr->owner_ptr;
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parent_ptr->has_iterator = winner_ptr->has_iterator;
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parent_ptr->current_iterator = winner_ptr->current_iterator;
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parent_ptr->end_iterator = winner_ptr->end_iterator;
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parent_ptr->source_node_ptr = winner_ptr;
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}
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/*
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pop the top node, factor it down the list to find its
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leaf, replace its leaf and then factor that back up
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*/
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template <class T, class owner_t, class iterator_t, class comparitor>
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void kmerge_tree_c<T, owner_t, iterator_t, comparitor>::next(void)
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{
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if ( top_node_ptr_mbr->current_iterator == top_node_ptr_mbr->end_iterator )
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{
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return;
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}
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// find the source leaf ptr
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node_rec* node_ptr = top_node_ptr_mbr;
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while ( node_ptr->source_node_ptr )
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{
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node_ptr = node_ptr->source_node_ptr;
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}
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// assert(!node_ptr->left_child_ptr && !node_ptr->right_child_ptr);
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// assert(top_node_ptr_mbr->current_iterator == node_ptr->current_iterator);
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++node_ptr->current_iterator;
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while ( node_ptr->parent_ptr )
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{
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compare_nodes(node_ptr);
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node_ptr = node_ptr->parent_ptr;
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}
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}
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#endif // KMERGE_TREE_H
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