堆排序中求前K个最小数

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01.#include "iostream"  02.#include "vector"  03.#include "algorithm"  04.using namespace std;  05.void HeapAdjust(std::vector<int> &a,int i,int size){ 06.    int lchild = 2*i + 1; 07.    int rchild = 2*i + 2;

 08.    int max = i;

09.    if(i < size/2 ){10.        if(lchild<size&&a[lchild]>a[max]) max = lchild;

 11.        if(lchild<size&&a[rchild]>a[max]) max = rchild; 12.        if(max != i){

13.            swap(a[i],a[max]);  14.            HeapAdjust(a,max,size);  15.        }  16.    }  17.}  18.void BuildHeap(std::vector<int> &a,int k){  19.    for (int i = k-1; i >= 0; --i)  20.    {  21.        HeapAdjust(a,i,k);  22.    }  23.}  24.int main(int argc, char const *argv[])  25.{  26.    std::vector<int> a(6);  27.    a[0] = 3;a[1] = 11; a[2] = 8;a[3] = 2;  28.    a[4] = 9;a[5] = 4;  29.    int k = 3;//取前k最小的  30.    BuildHeap(a,k);  31.    for (int i = k; i < a.size(); ++i)  32.    {  33.        if(a[0] > a[i]) {  34.            swap(a[0],a[i]);  35.            HeapAdjust(a,0,k);  36.        }  37.    }  38.    for (int i = 0; i < k; ++i)  39.    {  40.        cout<<a[i]<<"\t";  41.    }  42.    return 0;  43.}

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