数组中前k个数

class Solution {
public:
    vector<int> GetLeastNumbers_Solution(vector<int> input, int k) {
        
         vector<int> res;
        int size=input.size();
        if(input.size()==NULL||input.size()<k)
            return res;
        int start=0;
        int end=size-1;
        
        int mid=partion(input,start,end);
        
        while((k-1)!=mid){
            if((k-1)>mid){
                start=mid+1;
                mid=partion(input,start,end);
            }else{
                end=mid-1;
                mid=partion(input,start,end);
            }
            
        }
        
        for(int i=0;i<k;++i){
            res.push_back(input[i]);
        }
        
        return res;
    }
    
    int  partion(vector<int> &data,int l,int r){
        int i=l;
        int j=r;
        int key=data[i];
        
        while(i<j){
            
            while(i<j&&(data[j]>=key)){
                --j;
            }
            data[i]=data[j];
            
            while(i<j&&(data[i]<=key)){
                ++i;
            }
            data[j]=data[i];
        }
        data[i]=key;
        return i;
        
    }
};