代码笔记（c++）

 快速排序

void quicksort(vector&arr, int left, int right){
    if(left < right){
        int pivot = arr[left];
        int low = left, high = right;
        while(low < high){
            while(arr[high] >= pivot && low < high ){
                high--;
            }
            arr[low] = arr[high];  //因为pivot选在了最左侧，需先从右处理。
             while(arr[low] <= pivot && low < high ){
                low++;
            }
            arr[high] = arr[low];
        }
        arr[low] = pivot; //最后落脚很清晰。
        quicksort(arr,  left, low - 1);
        quicksort(arr,  low + 1, right);
    }
}

int main()
{
   vectortest{2,5,8,1,9,4,6};
   int n = test.size();
   quicksort(test, 0, n - 1);
   for(int i = 0 ; i < n ; ++i){
    cout << test[i] << " ";
   }

   return 0;

}