#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;
}

int order_statistic(int start, int end, int k)
{
    int mid = partition(start, end);

    if (start + k - 1 == mid)
    {
        return a[mid];
    }
    else if (start + k - 1 > mid)
    {
        return order_statistic(mid + 1, end, k - mid - 1);  // 0号位不用就不用减1了
    }
    else
    {
        return order_statistic(start, mid - 1, k);
    }
}

实在不明白你返回 a[mid-1] 是什么意思

[ 本帖最后由 azzbcc 于 2015-9-4 23:28 编辑 ]

在寻找第7小时会出错额