add heap algo

Author: LYDongD

go/28_heap/heap.go

@@ -1,7 +1,5 @@
 package heap
 
-import "fmt"
-
 type Heap struct {
 a []int
 n int
@@ -49,23 +47,29 @@ func (heap *Heap) removeMax() {
 swap(heap.a, 1, heap.count)
 heap.count--
 
-//comapre with left and right
-for i := 1; i <= heap.count/2; {
+//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 heap.a[i] < heap.a[i*2] {
+if a[i] < a[i*2] {
 maxIndex = i * 2
 }
 
-if i*2+1 <= heap.count && heap.a[maxIndex] < heap.a[i*2+1] {
+if i*2+1 <= count && a[maxIndex] < a[i*2+1] {
 maxIndex = i*2 + 1
 }
 
 if maxIndex == i {
 break
 }
 
-swap(heap.a, i, maxIndex)
+swap(a, i, maxIndex)
 i = maxIndex
 }
 

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
+}