From 4ea857183a71ac609dba19c2de618768ca748a22 Mon Sep 17 00:00:00 2001
From: Emir Pasic <emirpasic@hotmail.com>
Date: Wed, 7 Sep 2016 03:51:19 +0200
Subject: [PATCH] - optimization to bulk insert into heap as per @cristaloleg
 suggestion #32

---
 README.md                           |  4 +---
 trees/binaryheap/binaryheap.go      | 28 ++++++++++++++++++++++------
 trees/binaryheap/binaryheap_test.go | 13 +++++++++++++
 3 files changed, 36 insertions(+), 9 deletions(-)

diff --git a/README.md b/README.md
index 0534ddf..e1bdca6 100644
--- a/README.md
+++ b/README.md
@@ -710,9 +710,7 @@ func main() {
 		return -utils.IntComparator(a, b)
 	}
 	heap = binaryheap.NewWith(inverseIntComparator) // empty (min-heap)
-	heap.Push(2)                                    // 2
-	heap.Push(3)                                    // 3, 2
-	heap.Push(1)                                    // 3, 2, 1
+	heap.Push(2, 3, 1)                              // 3, 2, 1 (bulk optimized)
 	heap.Values()                                   // 3, 2, 1
 }
 ```
diff --git a/trees/binaryheap/binaryheap.go b/trees/binaryheap/binaryheap.go
index 0ba9284..70b28cf 100644
--- a/trees/binaryheap/binaryheap.go
+++ b/trees/binaryheap/binaryheap.go
@@ -45,9 +45,20 @@ func NewWithStringComparator() *Heap {
 }
 
 // Push adds a value onto the heap and bubbles it up accordingly.
-func (heap *Heap) Push(value interface{}) {
-	heap.list.Add(value)
-	heap.bubbleUp()
+func (heap *Heap) Push(values ...interface{}) {
+	if len(values) == 1 {
+		heap.list.Add(values[0])
+		heap.bubbleUp()
+	} else {
+		// Reference: https://en.wikipedia.org/wiki/Binary_heap#Building_a_heap
+		for _, value := range values {
+			heap.list.Add(value)
+		}
+		size := heap.list.Size()/2 + 1
+		for i := size; i >= 0; i-- {
+			heap.bubbleDownIndex(i)
+		}
+	}
 }
 
 // Pop removes top element on heap and returns it, or nil if heap is empty.
@@ -101,10 +112,15 @@ func (heap *Heap) String() string {
 	return str
 }
 
-// Performs the "bubble down" operation. This is to place the element that is at the
-// root of the heap in its correct place so that the heap maintains the min/max-heap order property.
+// Performs the "bubble down" operation. This is to place the element that is at the root
+// of the heap in its correct place so that the heap maintains the min/max-heap order property.
 func (heap *Heap) bubbleDown() {
-	index := 0
+	heap.bubbleDownIndex(0)
+}
+
+// Performs the "bubble down" operation. This is to place the element that is at the index
+// of the heap in its correct place so that the heap maintains the min/max-heap order property.
+func (heap *Heap) bubbleDownIndex(index int) {
 	size := heap.list.Size()
 	for leftIndex := index<<1 + 1; leftIndex < size; leftIndex = index<<1 + 1 {
 		rightIndex := index<<1 + 2
diff --git a/trees/binaryheap/binaryheap_test.go b/trees/binaryheap/binaryheap_test.go
index 36ce9f9..a20d647 100644
--- a/trees/binaryheap/binaryheap_test.go
+++ b/trees/binaryheap/binaryheap_test.go
@@ -34,6 +34,19 @@ func TestBinaryHeapPush(t *testing.T) {
 	}
 }
 
+func TestBinaryHeapPushBulk(t *testing.T) {
+	heap := NewWithIntComparator()
+
+	heap.Push(15, 20, 3, 1, 2)
+
+	if actualValue := heap.Values(); actualValue[0].(int) != 1 || actualValue[1].(int) != 2 || actualValue[2].(int) != 3 {
+		t.Errorf("Got %v expected %v", actualValue, "[1,2,3]")
+	}
+	if actualValue, ok := heap.Pop(); actualValue != 1 || !ok {
+		t.Errorf("Got %v expected %v", actualValue, 1)
+	}
+}
+
 func TestBinaryHeapPop(t *testing.T) {
 	heap := NewWithIntComparator()