LCR 159. 库存管理 III

这道题虽然简单，但是可以有多重解法，适合练习各种解法。

可以用基于快速排序思想的快速选择算法：

class Solution {
public:
    vector<int> inventoryManagement(vector<int>& stock, int cnt) {
        vector<int> res;
        int len = stock.size();
        quick_select(stock,0,len-1,cnt);
        for(int i = 0;i < cnt;i++)
            res.push_back(stock[i]);
        return res;
    }

    void quick_select(vector<int>& stock,int left,int right,int cnt)
    {
        if(left <= right)
        {
            int pos = partition(stock,left,right);
            if(pos == cnt - 1){
                return;
            }
            else if(pos > cnt -1){
                quick_select(stock,left,pos - 1,cnt);
            }
            else{
                quick_select(stock,pos + 1,right,cnt);
            }
        }
    }

    int partition(vector<int>& stock,int left,int right)
    {
        if(left >= right)
            return left;
        int pivot = stock[left];

        while(left < right){
            while(left<right&&stock[right] >= pivot) right--;
            stock[left] = stock[right];
            while(left<right&&stock[left]<= pivot) left++;
            stock[right] = stock[left];
        }
        stock[left] = pivot; 
        return left;
    }
};