数组中 最小K个数

Posted 2022-08-17 cgy1012

1 基于快排中 partition函数的思想

一定要注意那里是对容器的地址 或者引用操作 否则传不出来！！！

public:
    vector<int> GetLeastNumbers_Solution(vector<int> input, int k) 
 

vector<int> result;       
        if(input.empty() || k>input.size() || k<=0) return result;
         
        int start = 0;
        int end = input.size()-1;
        int index = partition(input,start,end);
         
        while(index != (k-1))
        
            if(index > (k-1))
            
                end = index - 1;
                index = partition(input,start,end);
            
            else
            
                start = index + 1;
                index = partition(input,start,end);
            
        
         
        for(int i=0;i<k;++i)
        
            result.push_back(input[i]);
        
         
        return result;
    
    
 int  partition(vector<int>  &numbers,int low,int high)
    
     int pivotkey=numbers[low];//当参考值

        while(low<high)
        
            while(low<high&&numbers[high]>pivotkey)
            high--;
            swap(numbers[low],numbers[high]);

           while(low<high&&numbers[low]<=pivotkey)
                low++;
            swap(numbers[low],numbers[high]);

        

        return low;

 

void swap(int &A,int &B)
 
 int temp;
 temp=A;
 A=B;
 B=temp;
  

 方法2  基于muiltiset   红黑树  最大堆排序

// ====================方法2====================
typedef multiset<int, greater<int> >            intSet;//greater函数和less相反，这个谓词
typedef multiset<int, greater<int> >::iterator  setIterator;//设置迭代器

void GetLeastNumbers_Solution2(const vector<int>& data, intSet& leastNumbers, int k)

    leastNumbers.clear();//清空

    if (k < 1 || data.size() < k)
        return;

    vector<int>::const_iterator iter = data.begin();//vector迭代器
    for (; iter != data.end(); ++iter)
    
        if ((leastNumbers.size()) < k)
            leastNumbers.insert(*iter);

        else
        
            setIterator iterGreatest = leastNumbers.begin();//multiset迭代器

            if (*iter < *(leastNumbers.begin()))
            
                leastNumbers.erase(iterGreatest);//删除该条目
                leastNumbers.insert(*iter);//插入新的，自动排序