A set is a data structure that can store elements and no repeated values. It is a computer implementation of the mathematical concept of a finite set. Unlike most other collection types, rather than retrieving a specific element from a set, one typically tests an element for membership in a set. This structed is often used to ensure that no duplicates are present in a collection.
All sets implement the set interface with the following methods:
```go
Add(items ...interface{})
Remove(items ...interface{})
Contains(items ...interface{}) bool
Empty() bool
Size() int
Clear()
Values() []interface{}
```
####HashSet
This structure implements the Set interface and is backed by a hash table (actually a Go's map). It makes no guarantees as to the iteration order of the set, since Go randomizes this iteration order on maps.
This structure offers constant time performance for the basic operations (add, remove, contains and size).
The stack interface represents a last-in-first-out (LIFO) collection of objects. The usual push and pop operations are provided, as well as a method to peek at the top item on the stack, a method to check whether the stack is empty and the size (number of elements).
All stacks implement the stack interface with the following methods:
```go
Push(value interface{})
Pop() (value interface{}, ok bool)
Peek() (value interface{}, ok bool)
Empty() bool
Size() int
Clear()
```
####LinkedListStack
This stack structure is based on a linked list, i.e. each previous element has a point to the next.
All operations are guaranted constant time performance.
Map structure based on our red-black tree implementation. Keys are ordered with respect to the passed comparator.
_Put()_, _Get()_ and _Remove()_ are guaranteed log(n) time performance.
_Key()_ and _Values()_ methods return keys and values respectively in order of the keys. These meethods are quaranteed linear time performance.
```go
package main
import "github.com/emirpasic/gods/maps/treemap"
func main() {
m := treemap.NewWithIntComparator() // empty (keys are of type int)
m.Put(1, "x") // 1->x
m.Put(2, "b") // 1->x, 2->b (in order)
m.Put(1, "a") // 1->a, 2->b (in order)
_, _ = m.Get(2) // b, true
_, _ = m.Get(3) // nil, false
_ = m.Values() // []interface {}{"a", "b"} (in order)
_ = m.Keys() // []interface {}{1, 2} (in order)
m.Remove(1) // 2->b
m.Clear() // empty
m.Empty() // true
m.Size() // 0
}
```
###Trees
A tree is a widely used data data structure that simulates a hierarchical tree structure, with a root value and subtrees of children, represented as a set of linked nodes; thus no cyclic links.
####RedBlackTree
A red–black tree is a binary search tree with an extra bit of data per node, its color, which can be either red or black. The extra bit of storage ensures an approximately balanced tree by constraining how nodes are colored from any path from the root to the leaf. Thus, it is a data structure which is a type of self-balancing binary search tree.[Wikipedia](http://en.wikipedia.org/wiki/Red%E2%80%93black_tree)
The balancing of the tree is not perfect but it is good enough to allow it to guarantee searching in O(log n) time, where n is the total number of elements in the tree. The insertion and deletion operations, along with the tree rearrangement and recoloring, are also performed in O(log n) time.[Wikipedia](http://en.wikipedia.org/wiki/Red%E2%80%93black_tree)
Various helper functions used throughout the library.
#### Comparator
Some data structures (e.g. TreeMap, TreeSet) require a comparator function to sort their contained elements. This comparator is necessary during the initalization.
Comparator is defined as:
```go
Return values:
-1, if a <b
0, if a == b
1, if a > b
Comparator signature:
type Comparator func(a, b interface{}) int
```
Two common comparators are included in the library:
#####IntComparator
```go
func IntComparator(a, b interface{}) int {
aInt := a.(int)
bInt := b.(int)
switch {
case aInt > bInt:
return 1
case aInt <bInt:
return -1
default:
return 0
}
}
```
#####StringComparator
```go
func StringComparator(a, b interface{}) int {
s1 := a.(string)
s2 := b.(string)
min := len(s2)
if len(s1) <len(s2){
min = len(s1)
}
diff := 0
for i := 0; i <min&&diff ==0;i++{
diff = int(s1[i]) - int(s2[i])
}
if diff == 0 {
diff = len(s1) - len(s2)
}
return diff
}
```
#####CustomComparator
```go
package main
import (
"fmt"
"github.com/emirpasic/gods/sets/treeset"
)
type User struct {
id int
name string
}
// Comparator function (sort by IDs)
func byID(a, b interface{}) int {
// Type assertion, program will panic if this is not respected
- Avoiding to consume memory by using optimal algorithms and data structures for the given set of problems, e.g. red-black tree in case of TreeMap to avoid keeping redundant sorted array of keys in memory.
There is often a tug of war between speed and memory when crafting algorithms. We choose to optimize for speed in most cases within reasonable limits on memory consumption.
