STL 之 partition()方法 和 stable_partition()方法

转自：https://blog.csdn.net/godenlove007/article/details/7982307

这两个方法都用来将指定容器的元素根据指定的predicate函数分成两个子序列，其中满足predicate()函数的，返回值为true的作为第一个序列[v.begin(), bound), 而[bound, v.end())的作为第二个序列。两个方法的区别在于， partition()对于两个子序列中的元素并不排序，而stable_partition()则对两个子序列的元素也进行排序。

BidirectionalIterator partition ( BidirectionalIterator first, BidirectionalIterator last, Predicate pred );
BidirectionalIterator stable_partition ( BidirectionalIterator first, BidirectionalIterator last, Predicate pred );
Parameters:
first, last 第一个和第二个参数说明给定源容器的范围 [first, last)
pred 第三个参数给定进行分组的规则函数 布尔型返回值 对于返回true的所有元素作为第一个子序列，对于返回false的所有元素作为第二个子序列
Return value 返回值是 指向第二个子序列的首元素迭代器

#include <iostream>
 #include <vector>
 #include <algorithm>
 
 using namespace std;
 
 bool IsOdd(int i)
 {
     return (i%2 == 1);
 }
 
 int main()
 {
     vector<int> v = {2,6,3,8,4,5,9,7,1,0};
 
     cout<<"The original elements in the vector are: "<<endl;
     vector<int>::iterator it, bound;
 
     for(it = v.begin(); it != v.end(); it++)
         cout<<*it<<" ";
     cout<<endl;
 
     cout<<"First use the function partition() to separate all elements into 2 groups without ordering: "<<endl;
     //use partition to separate the vector into 2 parts...
     bound = partition(v.begin(), v.end(), IsOdd);
 
     cout << "All odd elements in the vector are:" <<endl;
     for(it = v.begin(); it != bound; it++)
         cout<<*it<<" ";
     cout<<endl;
 
     cout<< "All even elements in the vector are:" <<endl;
     for(it = bound; it != v.end(); it++)
         cout<<*it<<" ";
     cout<<endl;
 
     v.clear();
     for(int i = 0; i < 10; i++)
     v.push_back(i);
 
     cout<<"Secondly use the function stable_partition() to separate all elements into 2 groups with ordering: "<<endl;
     //use stable_partition to separate the vector into 2 parts...
     bound = stable_partition(v.begin(), v.end(), IsOdd);
     
         cout << "All odd elements in the vector are:" <<endl;
     for(it = v.begin(); it != bound; it++)
         cout<<*it<<" ";
     cout<<endl;
 
     cout<< "All even elements in the vector are:" <<endl;
     for(it = bound; it != v.end(); it++)
         cout<<*it<<" ";
     cout<<endl;
     
     return 0;
 }

输出：

The original elements in the vector are:
2 6 3 8 4 5 9 7 1 0
First use the function partition() to separate all elements into 2 groups without ordering:
All odd elements in the vector are:
1 7 3 9 5
All even elements in the vector are:
4 8 6 2 0
Secondly use the function stable_partition() to separate all elements into 2 groups with ordering:
All odd elements in the vector are:
3 5 9 7 1
All even elements in the vector are:
2 6 8 4 0

可以看到，stable函数可以保证在分类过程中不改变原来同一类元素的相对位置。