std::includes() in C++ STL

C++ defines a function which can be used to recognise if all the numbers in a container, also exists in other container. This task can be achieved by using “includes()” which is defined in “algorithm” header. The implementations are explained below.

Syntax 1 : Using operator “<"

Template :
template 
  bool includes (initer1 beg1, initer1 end1,
                        initer2 beg2, initer2 end2,)
Parameters :
beg1 :  Input iterator to initial position of first sorted sequence.
end1 :  Input iterator to final position of first sorted sequence.

beg2 :  Input iterator to initial position of second sorted sequence.
end2 :  Input iterator to final position of second sorted sequence.

Return value : 
True if every element of 2nd container lies in 1st container.

// C++ code to demonstrate the working of  
// includes() implementation 1 
  
#include<bits/stdc++.h> 
using namespace std; 
  
int main() 
{ 
    // initializing 1st container 
    vector<int> arr1 = { 1, 4, 6, 3, 2 }; 
      
    // initializing 2nd container 
    vector<int> arr2 = { 1, 2, 4 }; 
      
    // sorting initial containers 
    sort(arr1.begin(), arr1.end()); 
    sort(arr2.begin(), arr2.end()); 
      
    // using include() check if all elements  
    // of arr2 lie in arr1  
    if(includes(arr1.begin(), arr1.end(), arr2.begin(), arr2.end())) 
    cout << "All elements of 2nd container are in 1st container"; 
    else 
    cout << "All elements of 2nd container are not in 1st container"; 
      
} 

Output :

All elements of 2nd container are in 1st container

Syntax 2 : Using Comparator

Template :
template 
  bool includes (initer1 beg1, initer1 end1,
                        initer2 beg2, initer2 end2, Compare comp)
Parameters :
beg1 :  Input iterator to initial position of first sorted sequence.
end1 :  Input iterator to final position of first sorted sequence.

beg2 :  Input iterator to initial position of second sorted sequence.
end2 :  Input iterator to final position of second sorted sequence.

comp : The comparator function that returns a boolean
true/false of the each elements compared. This function 
accepts two arguments. This can be function pointer or 
function object and cannot change values.

Return value : 
True if every element of 2nd container lies in 1st container.

// C++ code to demonstrate the working of  
// includes() implementation 2 
  
#include<bits/stdc++.h> 
using namespace std; 
  
// comparator function 
bool comp (int i, int j) { return i<j; } 
  
int main() 
{ 
    // initializing 1st container 
    vector<int> arr1 = { 1, 4, 6, 3, 2 }; 
      
    // initializing 2nd container 
    vector<int> arr2 = { 1, 2, 4 }; 
      
    // sorting initial containers 
    sort(arr1.begin(), arr1.end()); 
    sort(arr2.begin(), arr2.end()); 
      
    // using include() check if all elements  
    // of arr2 lie in arr1  
    // using comparator function 
    if(includes(arr1.begin(), arr1.end(), arr2.begin(), arr2.end(), comp)) 
    cout << "All elements of 2nd container are in 1st container"; 
    else 
    cout << "All elements of 2nd container are not in 1st container"; 
      
} 

Output:

All elements of 2nd container are in 1st container

Possible application : This function can be potentially used to find if a set is subset of another or can be used to determine lottery winner , in a system in which person who has all the lottery numbers in his card wins the lottery. Latter one is explained below through code.

// C++ code to demonstrate the application of  
// includes()  
  
#include<bits/stdc++.h> 
using namespace std; 
  
int main() 
{ 
    // lottery numbers 
    vector<int> lottery = { 1, 4, 6, 3, 2, 54 , 32 }; 
      
    // Numbers in user's card 
    vector<int> user = { 1, 2, 4, 6 }; 
      
    // sorting initial containers 
    sort(lottery.begin(), lottery.end()); 
    sort(user.begin(), user.end()); 
      
    // using include() check if all elements  
    // of user are present as lottery numbers 
    if(includes(lottery.begin(), lottery.end(), user.begin(), user.end())) 
    cout << "User has won lottery ( all numbers are lottey numbers )"; 
    else 
    cout << "User has not won the lottery"; 
      
} 

This article is contributed by Manjeet Singh. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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