Sword Finger Offer Interview Question 40. Minimum k Number [Simple]-Quick Sort

My solution:

1. Use sort () to sort the vector, insert the first k elements into vector <int> res

class Solution {
public:
    vector<int> getLeastNumbers(vector<int>& arr, int k) {
        vector<int> res;
        if(arr.empty()) return res;
        sort(arr.begin(),arr.end());
        for(int i=0;i<k;i++)
            res.push_back(arr[i]);
        return res;
    }
};

2. Quick Sort

Compare the number of elements on the left of pivot with K in quick sort

It should be noted that, but k> this number is needed, and the right side of the array needs to be sorted, the value of k needs to be changed (stuck here for a long time)

quicksort(nums,i+1,r,k-i+l-1)

class Solution {
public:
    void quicksort(vector<int>&nums,int l,int r,int k){
        if(l>=r) return;
        int i=l,j=r;
        int pivot=nums[l];
        while(i<j){
            while(nums[j]>=pivot&&i<j)  j--;
            if(i<j) nums[i++]=nums[j];
            while(nums[i]<=pivot&&i<j)  i++;
            if(i<j) nums[j--]=nums[i];
        }
        nums[i]=pivot;
        if(i-l+1==k)    return;
        if(k>i-l+1) quicksort(nums,i+1,r,k-i+l-1);
        else if(k<i-l+1)    quicksort(nums,l,i-1,k);
    }

    vector<int> getLeastNumbers(vector<int>& arr, int k) {
        vector<int> res;
        if(arr.empty()) return res;
        quicksort(arr,0,arr.size()-1,k);
        for(int i=0;i<k;i++)
            res.push_back(arr[i]);
        return res;
    }
};