快排

void mysort(vector<int>& nums, int l, int r){
    if(l>=r) return;
    int tl = l;
    int tr = r;

    int flag = nums[l];
    while(l<r){

        while(l<r&&flag<=nums[r]){
            r--;
        }
        nums[l] = nums[r];
        while(l<r&&nums[l]<=flag){
            l ++;
        }
        nums[r] = nums[l];
    }
    nums[l] = flag;

    mysort(nums, tl, l-1);
    mysort(nums, l+1, tr);
}