Merge pull request #175 from LYDongD/master

add heap algo in golang

Author: wangzheng0822

go/28_heap/heap.go

@@ -0,0 +1,83 @@
+package heap
+
+type Heap struct {
+	a     []int
+	n     int
+	count int
+}
+
+//init heap
+func NewHeap(capacity int) *Heap {
+	heap := &Heap{}
+	heap.n = capacity
+	heap.a = make([]int, capacity+1)
+	heap.count = 0
+	return heap
+}
+
+//top-max heap -> heapify from down to up
+func (heap *Heap) insert(data int) {
+	//defensive
+	if heap.count == heap.n {
+		return
+	}
+
+	heap.count++
+	heap.a[heap.count] = data
+
+	//compare with parent node
+	i := heap.count
+	parent := i / 2
+	for parent > 0 && heap.a[parent] < heap.a[i] {
+		swap(heap.a, parent, i)
+		i = parent
+		parent = i / 2
+	}
+}
+
+//heapfify from up to down
+func (heap *Heap) removeMax() {
+
+	//defensive
+	if heap.count == 0 {
+		return
+	}
+
+	//swap max and last
+	swap(heap.a, 1, heap.count)
+	heap.count--
+
+	//heapify from up to down
+	heapifyUpToDown(heap.a, heap.count)
+}
+
+//heapify
+func heapifyUpToDown(a []int, count int) {
+
+	for i := 1; i <= count/2; {
+
+		maxIndex := i
+		if a[i] < a[i*2] {
+			maxIndex = i * 2
+		}
+
+		if i*2+1 <= count && a[maxIndex] < a[i*2+1] {
+			maxIndex = i*2 + 1
+		}
+
+		if maxIndex == i {
+			break
+		}
+
+		swap(a, i, maxIndex)
+		i = maxIndex
+	}
+
+}
+
+//swap two elements
+func swap(a []int, i int, j int) {
+	tmp := a[i]
+	a[i] = a[j]
+	a[j] = tmp
+}

go/28_heap/heap_sort.go

@@ -0,0 +1,54 @@
+package heap
+
+//build a heap
+func buidHeap(a []int, n int) {
+
+	//heapify from the last parent node
+	for i := n / 2; i >= 1; i-- {
+		heapifyUpToDown(a, i, n)
+	}
+
+}
+
+//sort by ascend, a index begin from 1, has n elements
+func sort(a []int, n int) {
+	buidHeap(a, n)
+
+	k := n
+	for k >= 1 {
+		swap(a, 1, k)
+		heapifyUpToDown(a, 1, k-1)
+		k--
+	}
+}
+
+//heapify from up to down , node index = top
+func heapifyUpToDown(a []int, top int, count int) {
+
+	for i := top; i <= count/2; {
+
+		maxIndex := i
+		if a[i] < a[i*2] {
+			maxIndex = i * 2
+		}
+
+		if i*2+1 <= count && a[maxIndex] < a[i*2+1] {
+			maxIndex = i*2 + 1
+		}
+
+		if maxIndex == i {
+			break
+		}
+
+		swap(a, i, maxIndex)
+		i = maxIndex
+	}
+
+}
+
+//swap two elements
+func swap(a []int, i int, j int) {
+	tmp := a[i]
+	a[i] = a[j]
+	a[j] = tmp
+}