最小K个数--------------快排partition应用

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题目描述
输入n个整数，找出其中最小的K个数。例如输入4,5,1,6,2,7,3,8这8个数字，则最小的4个数字是1,2,3,4,。

手撕:

#include<iostream>
#include<vector>
using namespace std;

//快排核心partition
int myPartition(vector<int>& vr,int beg,int end){
    int left=beg;
    int right=end;
    int cur=vr[beg];
    while(left<right){
        while(right>left&&vr[right]>=cur)right--;
        swap(vr[right],vr[left]);
        while(left<right&&vr[left]<=cur)left++;
        swap(vr[left],vr[right]);
    }
    vr[left]=cur;
    return left;
}
//快排
void quickSort(vector<int>& vr,int beg,int end){
    if(end>beg){
        int mid=myPartition(vr,beg,end);
        quickSort(vr,beg,mid);
        quickSort(vr,mid+1,end);
    }
}
//本题
vector<int> GetLeastNumbers_Solution(vector<int> input, int k) {
    vector<int>res;
    int size=input.size();
    if(size&&k>0&&k<=size){
        int beg=0;
        int end=size-1;
        int t=k;        
        int mid=-1;
        while(mid!=t-1){
            mid=myPartition(input,beg,end);
            if(mid==t-1){
                for(int i=0;i<k;++i){
                    res.push_back(input[i]);                    
                }
                break;
            }else if(mid>t-1){
                end=mid;
            }else{
                beg=mid;
                t=t-(mid+1);
            }
        }
    }
    return res;
}

测试:
int main(){
    int a[]={4,5,1,6,2,7,3,8};
    vector<int>vr(a,end(a));
    GetLeastNumbers_Solution(vr,4);
    return 0;
}

题目来源:
https://www.nowcoder.com/practice/6a296eb82cf844ca8539b57c23e6e9bf?tpId=13&tqId=11182&tPage=2&rp=2&ru=/ta/coding-interviews&qru=/ta/coding-interviews/question-ranking