快速排序

int partition(vector<int>&arr, int begin, int end)
{
    int pivot = arr[begin];
    while(begin < end)
    {
        while(begin < end && arr[--end] >= pivot);
        arr[begin] = arr[end];
        while(begin < end && arr[++begin] <= pivot);
        arr[end] = arr[begin];
    }
    arr[begin] = pivot;
    return begin;
}


void quick_sort(vector<int> &arr, int begin, int end){
    if(begin >= end - 1){
        return;
    }
    int pos = partition(arr, begin, end);
    quick_sort(arr, begin, pos);
    quick_sort(arr, pos+1, end);
}