最小的k个数

 // 最小的k个数.cpp : 定义控制台应用程序的入口点。
 //

 #include "stdafx.h"
 #include <iostream>
 #include <set>
 #include <vector>
 #include <queue>
 using namespace std;

 //  set中默认是从大到小的顺序，即最先取出的是最小值
 //  此处为从小到大，最先取出的是最大值
 typedef multiset<int,greater<int>> inSet;
 typedef multiset<int,greater<int>>::iterator setIterator;

 //  基于红黑树
 void GetNumber(vector<int> &data,inSet &leastNumber,int k)
 {
     if(k<= || data.size()==)
         return ;
     leastNumber.clear();
     vector<int>::iterator it = data.begin();
     for(;it!=data.end();++it)
     {
         if(leastNumber.size()<k)
             leastNumber.insert(*it);
         else{
             setIterator s = leastNumber.begin();

             if(*it < *s)
             {
                 leastNumber.erase(s);
                 leastNumber.insert(*it);
             }
         }
     }
     setIterator s = least.begin();
     for(;s!=least.end();++s)
         cout<<*s<<" ";
     cout<<endl;
 }

 //  基于优先队列
 void GetNumber2(vector<int> &data,int k)
 {
     if(data.size()== || k<)
         return ;
     //  top取出的是最小值，即是按从大到小排列的
     //priority_queue<int,vector<int>,greater<int>> q;
     // 默认是从小到大排列，即最先取出的是最大值
     priority_queue<int> q;
     vector<int>::iterator it = data.begin();
     for(;it!=data.end();++it)
     {
         if(q.size()<k)
             q.push(*it);
         else{
             if(*it < q.top())
             {
                 q.pop();
                 q.push((*it));
             }
         }
     }
     while(q.size()>)
     {
         cout<<q.top()<<" ";
         q.pop();
     }
     cout<<endl;
 }

 int Partition(int *a,int start,int end)
 {
     if(start < end)
     {
         int i=start,j=end;
         int x = a[start];
         while(i<j)
         {
             while(i<j && a[j]>x)
                 j--;
             if(i<j)
                 a[i++] = a[j];
             while(i<j && a[i]<x)
                 i++;
             if(i<j)
                 a[j--] = a[i];
         }
         a[i] = x;
         return i;
     }
 }

 //  基于分治思想，但会修改数组，时间复杂度为O(N)
 void GetNumber2(int *a,int len,int k)
 {
     if(a==NULL || len<= || k<=)
         return ;
     int start = ,end = len-;
     int index = Partition(a,start,end);
         //取出最小的K个数
     while(index != k-)
     {
         if(index < k-)
         {
             start = index +;
             index = Partition(a,start,end);
         }else{
             end = index -;
             index = Partition(a,start,end);
         }
     }
     for(int i=;i<k;++i)
         cout<<a[i]<<" ";
     cout<<endl;
 }

 int _tmain(int argc, _TCHAR* argv[])
 {
     vector<int> v;
     v.push_back();
     v.push_back();
     v.push_back();
     v.push_back();
     v.push_back();
     v.push_back();
     v.push_back();
     inSet least;
     GetNumber1(v,least,);

     GetNumber2(v,);

     int a[]={,,,,,,,};
     GetNumber2(a,,);

     system("pause");
     return ;
 }