fixed heap: index of parent bug

Author: legolas.zhan

data-structure/heap/heap.go

@@ -67,10 +67,10 @@ func (h *Heap) Peek() (e Element) {
 
 func (h *Heap) precolateUp(index int) {
 	// 上滤，新元素在堆中上滤直到找出正确位置
-	needUp, parent := index, index>>1
+	needUp, parent := index, (index-1)>>1
 	for needUp > 0 && h.less(h.heap[needUp], h.heap[parent]) {
 		h.heap[parent], h.heap[needUp] = h.heap[needUp], h.heap[parent]
-		needUp, parent = parent, parent>>1
+		needUp, parent = parent, (parent-1)>>1
 	}
 }
 

data-structure/heap/heap_test.go

@@ -1,8 +1,10 @@
 package heap
 
 import (
-	"github.com/stretchr/testify/assert"
+	"fmt"
 	"testing"
+
+	"github.com/stretchr/testify/assert"
 )
 
 type Int int
@@ -39,6 +41,28 @@ func Test_MinHeap(t *testing.T) {
 	}
 }
 
+// leetcode s215 bug
+func Test_MinHeap_2(t *testing.T) {
+	assert := assert.New(t)
+
+	h := New(true)
+	for _, num := range []Int{-7576, 4209, 9414, 5451, -5927, 5860, -1170, -8248, 4803, 9364, -2880, -3983, 3463,
+		-555, 7491, 6544, 1671, 4898, -4888, -5685, 1488, 1072, -3841, 7299, -991, -5525, -197,
+		-2082, -7256, 1134, -9602, 9398, 2097, 9831, -1377, 8362, -1476, -5141, 9906, -7646,
+	} {
+		h.Insert(num)
+	}
+
+	res := make([]int, 0, h.Len())
+	for h.Len() > 0 {
+		res = append(res, int(h.Extract().(Int)))
+	}
+
+	for i := 0; i < len(res)-1; i++ {
+		assert.True(res[i] <= res[i+1], fmt.Sprintf("error at i={%d}", i))
+	}
+}
+
 func Test_MaxHeap(t *testing.T) {
 	assert := assert.New(t)
 
@@ -102,3 +126,22 @@ func Test_precolate(t *testing.T) {
 		assert.True(res[i] < res[i+1])
 	}
 }
+
+func Test_cal_parent_index(t *testing.T) {
+	assert := assert.New(t)
+
+	for index := 0; index < 10; index++ {
+		if index%2 == 0 {
+			assert.NotEqual((index-1)>>1, index>>1, fmt.Sprintf("index={%d}", index))
+		} else {
+			assert.Equal((index-1)>>1, index>>1, fmt.Sprintf("index={%d}", index))
+		}
+	}
+}
+
+func Test_cal_child_index(t *testing.T) {
+	assert := assert.New(t)
+	for index := 0; index < 100; index++ {
+		assert.Equal(index*2+1, index<<1+1, fmt.Sprintf("index={%d}", index))
+	}
+}

leetcode/heap/findKthLargest.go

@@ -9,6 +9,7 @@ You may assume k is always valid, 1 ≤ k ≤ array's length.
 
 package lheap
 
+/*
 // 快速选择算法
 func findKthLargest(nums []int, k int) int {
 	if len(nums) == 1 {
@@ -32,8 +33,8 @@ func findKthLargest(nums []int, k int) int {
 	}
 	return findKthLargest(nums[idx+1:], k-idx-1)
 }
+*/
 
-/*
 // 基于堆的实现
 import "github.com/TTWShell/algorithms/data-structure/heap"
 
@@ -59,4 +60,3 @@ func findKthLargest(nums []int, k int) int {
 	}
 	return int(heap.Peek().(findKthLargestInt))
 }
-*/