【剑指 offer】—— 快速排序

两个辅助函数：

// 生成区间内的随机整数int RandInRange(int s, int e, unsigned seed=time_t(0)){     srand(seed);    return rand()%(e-s)+s;}void Swap(int& a, int& b){    int tmp = a; a = b; b = tmp;}

分区函数：

int partition(int seq[], int len, int start, int end){    if (seq == NULL || len <= 0 || start < 0 || end >= len)        throw new exception("Invalid parameters");    int pivot = RandInRange(start, end);    Swap(seq[pivot], seq[end]);    int small = start - 1;    for (int i = start; i < end; ++i)    {        if (seq[i] < seq[end])          {            ++small;            if (small != i)                Swap(seq[small], seq[i]);        }    }    ++small;    Swap(seq[end], seq[small]);    return small;}

主调函数，由递归结构定义：

void qsort(int seq[], int len, int start, int end){    if (start == end)        return;    int idx = partition(seq, len, start, end);    if (idx > start)        qsort(seq, len, start, idx-1);    if (idx < end)        qsort(seq, len, idx+1, end);}