• go快排计算最小k个数和第k大的数


    计算最小的k个数,除了用堆,还可以用快排

    每次返回left right相遇的位置,index>k 则向左搜,index<k 向右搜,直到index==k

    剑指40 最小k个数(没要求顺序)
    • golang快排
    func getLeastNumbers(arr []int, k int) []int {
        if k==0{
            return []int{}
        }
        index:=Fast(arr,0,len(arr)-1,k)
        for index!=k-1{
            if index>k-1{
                index = Fast(arr,0,index-1,k)
            }else{
                index = Fast(arr,index+1,len(arr)-1,k)
            }
        }
        res:=make([]int,index+1)
        copy(res,arr[:index+1])
        return res
    }
    
    func Fast(nums []int,low,high,k int)int {
        start:=low
        end:=high
        tmp:=nums[low]
    
        for start<end{
            for start<end&&nums[end]>=tmp{
                end--
            }
            nums[start] = nums[end]
    
            for start<end&&nums[start]<=tmp{
                start++
            }
            nums[end] = nums[start]
        }
        nums[start] = tmp
        return start
    }
     
    
    • c++版本
     vector<int> GetLeastNumbers_Solution(vector<int> input, int k) {
            if(input.size()<k||k==0) return {};
           
            int index = fast(input,0,input.size()-1);
            while(index!=k-1)
            {
                if(index>k-1)
                    index = fast(input,0,index-1);
                else
                    index = fast(input,index+1,input.size()-1);
            }
            return vector<int>(input.begin(),input.begin()+k);
        }
        int fast(vector<int>&arr,int low,int high)
        {
            if(low>=high)return low;
            int start = low;
            int end = high;
            int tmp = arr[low];
            
            while(start<end)
            {
                while(start<end&&arr[end]>=tmp) end--;
                arr[start] = arr[end];
                while(start<end&&arr[start]<=tmp) start++;
                arr[end] = arr[start];
            }
            arr[start] = tmp;
            return start;
        }
    
    leetcode 215 第k个最大元素
    func findKthLargest(nums []int, k int) int {
        return Fast(nums,0,len(nums)-1,k)
    }
    
    func Fast(nums []int,low,high,k int)int  {
    
        start:=low
        end:=high
        tmp:=nums[low]
        for start<end{
            for start<end&&nums[end]<=tmp{
                end--
            }
            nums[start] = nums[end]
            for start<end&&nums[start]>=tmp{
                start++
            }
            nums[end] = nums[start]
        }
        nums[start] = tmp
        if start==k-1{
            return nums[k-1]
        }else if start>k-1{
            return Fast(nums,low,start-1,k)
        }else{
            return Fast(nums,start+1,high,k)
        }
    }
    
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  • 原文地址:https://www.cnblogs.com/9527s/p/14343715.html
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