BM46 最小的K个数

https://www.nowcoder.com/practice/6a296eb82cf844ca8539b57c23e6e9bf?tpId=295&tqId=23263&ru=%2Fpractice%2F253d2c59ec3e4bc68da16833f79a38e4&qru=%2Fta%2Fformat-top101%2Fquestion-ranking&sourceUrl=%2Fexam%2Foj%3Fpage%3D1%26tab%3D%25E7%25AE%2597%25E6%25B3%2595%25E7%25AF%2587%26topicId%3D295

思路： 构建最小堆，依次取出前k个。 构建最小堆的时候每次插入元素后要向上调整，取出最小元素后要向下调整。

 

package main

/**

* 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可

*

* @param input int整型一维数组

* @param k int整型

* @return int整型一维数组

*/

var index int

func adjustHeap(arr []int, len int) {

for i := (len - 1) / 2; i >= 0; {

if arr[i] > arr[len] {

tmp := arr[i]

arr[i] = arr[len]

arr[len] = tmp

len = i

if i == 0 {

break

}

i = (i - 1) / 2

} else {

break

}

}

}

func top(arr []int) int {

result := arr[0]

arr[0] = arr[index]

arr[index] = 2000

index--

//从上往下调整

i := 0

for arr[i] >= 0 {

if arr[i*2+1] > 1000 {

break

}

if arr[i*2+1] <= arr[i*2+2] && arr[i] > arr[i*2+1] {

tmp := arr[i]

arr[i] = arr[i*2+1]

arr[i*2+1] = tmp

i = i*2 + 1

continue

}

if arr[i*2+1] > arr[i*2+2] && arr[i] > arr[i*2+2] {

tmp := arr[i]

arr[i] = arr[i*2+2]

arr[i*2+2] = tmp

i = i*2 + 2

continue

}

break

}

return result

}

func GetLeastNumbers_Solution(input []int, k int) []int {

// write code here

result := make([]int, 0)

if k == 0 || len(input) == 0 {

return result

}

if k > len(input) {

return input

}

heapSize := 2*len(input) + 1

minHeap := make([]int, heapSize)

for i := 0; i < len(minHeap); i++ {

minHeap[i] = 2000

}

minHeap[0] = input[0]

//构建最小堆

for i := 1; i < len(input); i++ {

minHeap[i] = input[i]

adjustHeap(minHeap, i)

}

index = len(input) - 1

//取出前k个最小值

for i := 0; i < k; i++ {

result = append(result, top(minHeap))

}

return result

}