STL algorithm算法is_permutation(27)

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本文详细介绍了C++标准库中的is_permutation函数，包括其原型、用法及如何判断两个序列是否为同一元素集的不同排列。并通过示例展示了不同类型容器间的使用情况。

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is_permutation原型：

std::is_permutation

equality (1)	template <class ForwardIterator1, class ForwardIterator2> bool is_permutation (ForwardIterator1 first1, ForwardIterator1 last1, ForwardIterator2 first2);
predicate (2)	template <class ForwardIterator1, class ForwardIterator2, class BinaryPredicate> bool is_permutation (ForwardIterator1 first1, ForwardIterator1 last1, ForwardIterator2 first2, BinaryPredicate pred);

equality (1)

template <class ForwardIterator1, class ForwardIterator2>
   bool is_permutation (ForwardIterator1 first1, ForwardIterator1 last1,
                        ForwardIterator2 first2);

predicate (2)

template <class ForwardIterator1, class ForwardIterator2, class BinaryPredicate>
   bool is_permutation (ForwardIterator1 first1, ForwardIterator1 last1,
                        ForwardIterator2 first2, BinaryPredicate pred);

该函数是用来判断两个序列是否为同一元素集的不同排列！

该函数使用operator==或者是pred来判断两个元素是否是相等的。

其行为类似：

template <class InputIterator1, class InputIterator2>
  bool is_permutation (InputIterator1 first1, InputIterator1 last1,
                       InputIterator2 first2)
{
  std::tie (first1,first2) = std::mismatch (first1,last1,first2);
  if (first1==last1) return true;
  InputIterator2 last2 = first2; std::advance (last2,std::distance(first1,last1));
  for (InputIterator1 it1=first1; it1!=last1; ++it1) {
    if (std::find(first1,it1,*it1)==it1) {
      auto n = std::count (first2,last2,*it1);
      if (n==0 || std::count (it1,last1,*it1)!=n) return false;
    }
  }
  return true;
}

坑的是windows下面的codeblock居然不支持这个函数，我汗！

一个简单的测试例子：

#include <iostream>  
#include <vector>  
#include <array>  
#include <algorithm>  
using namespace std;  
int main(){  
    vector<int> v1{1,2,3,4,5,6};  
    vector<int> v2{1,5,6,4,3,2};  
    vector<int> v3{1,3,2,5,6,4,1};//add a elements 1  
    vector<double> v4{1,2,4,3,5,6};  
	vector<int> v5{1,0,2,3,4,5,6};
    array<int,6> ai{6,5,3,4,2,1};  
  
    cout<<"v1=";  
    for(int &i:v1)  
        cout<<i<<" ";  
    cout<<endl;  
     cout<<"v2=";  
    for(int &i:v2)  
        cout<<i<<" ";  
    cout<<endl;  
   cout<<"v3=";  
    for(int &i:v3)  
        cout<<i<<" ";  
    cout<<endl;  
   cout<<"v4=";  
    for(double &i:v4)  
        cout<<i<<" ";  
    cout<<endl;  
	 cout<<"v5=";  
    for(int &i:v5)  
        cout<<i<<" ";  
    cout<<endl;
   cout<<"ai=";  
    for(int &i:ai)  
        cout<<i<<" ";  
    cout<<endl;  
    if(is_permutation(v1.begin(),v1.end(),v2.begin()))
		cout<<"Yes ,v1 and v2 is permutation!"<<endl; 
	else
		cout<<"No ,v1 and v2 is not permutation!"<<endl; 		 
	
	if(is_permutation(v1.begin(),v1.end(),v3.begin()))
		cout<<"Yes ,v1 and v3 is permutation!"<<endl; 
	else
		cout<<"No ,v1 and v3 is not permutation!"<<endl; 

	if(is_permutation(v1.begin(),v1.end(),v4.begin()))
		cout<<"Yes ,v1 and v4 is permutation!"<<endl; 
	else
		cout<<"No ,v1 and v4 is not permutation!"<<endl; 

	if(is_permutation(v1.begin(),v1.end(),v5.begin()))
		cout<<"Yes ,v1 and v5 is permutation!"<<endl; 
	else
		cout<<"No ,v1 and v5 is not permutation!"<<endl; 

	if(is_permutation(v1.begin(),v1.end(),ai.begin()))
		cout<<"Yes ,v1 and ai is permutation!"<<endl; 
	else
		cout<<"No ,v1 and ai is not permutation!"<<endl; 
  
  
}

运行的结果：

可以看到，虽然v3多了一个元素1,但是v1和v3还是属于同一元素集的不同排列！