快速排序
void quick_sort(int q[], int l, int r)
{
if (l >= r)return;
int i = l - 1, j = r + 1, x = q[l + r >> 1];
while (i < j)
{
do i++; while (q[i] < x);
do j--; while (q[j] > x);
if (i < j) swap(q[i], q[j]);
}
quick_sort(q, l, j), quick_sort(q, j + 1, r);
}