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"; } |
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