C语言求第k小数快速排序思想

#include <iostream>

void input();
void QuickSelect(int *b, int left, int right, int target);
void swap(int i, int j);
void output();

int n;
int k;
int *a;

int main()
{
    input();
    QuickSelect(a, 0, n - 1, k);
    output();
    return 0;
}

void input()
{
    std::cin >> n;
    a = (int *)malloc(n * sizeof(int));
    for (int i = 0; i < n;i++)
    {
        std::cin >> a[i];
    }
    std::cin >> k;
}

void QuickSelect(int *b,int left,int right,int target)
{
    int i = left;
    int j = right;
    int tmp = left;
    while(i!=j)
    {
        while(i<j&&b[j]>=b[tmp])
            j--;
        while(i<j&&b[i]<=b[tmp])
            i++;
        swap(i, j);
    }
    swap(i, tmp);
    if((i-left+1)< target )
        QuickSelect(a, i + 1, right, target-i+left-1);
    if((i-left+1)>target)
        QuickSelect(a, left, i - 1, target);
}

void swap(int i,int j)
{
    int tmp = a[i];
    a[i] = a[j];
    a[j] = tmp;
}

void output()
{
    std::cout << a[k - 1]<<std::endl;
}