#include <stdio.h>
#define LEN 8

int a[LEN] = {1, 46, 7, 32, 75, 34, 678, 35};

int partition(int start, int end)
{
    int i = start;
    int j = end;
    int pivot = a[start];

    while (i < j){
        while (i < j && pivot <= a[j])
            j--;
        a[i] = a[j];
        while (i < j && pivot >a[i])
            i++;
        a[j] = a[i];
    }
    a[i] = pivot;
    return i;
}

int order_statistic(int start, int end ,int k)
{
    int mid ;
    mid = partition(start, end);                    //用partition函数把序列分成两半，中间的pivot元素是序列中的第i个;
    if(k == mid)
        return a[mid-1];                            //返回找到的元素;
    else if(k > mid)
        order_statistic(mid+1, end , k-mid);            //从后半部分找出第k-i小的元素并返回;
    else
        order_statistic(start, mid-1, k);            //从前半部分找出第k小的元素并返回;
}

int main(void)
{
    int value;
    int i;
    value = order_statistic(0, LEN-1, 3);
    printf("%d\n", value);
    for(i = 0; i < LEN; i++)
        printf("%d ", a[i]);
    return 0;
}

在寻找第7小时会出错额