Open In App

std::gcd | C++ inbuilt function for finding GCD

Improve
Improve
Like Article
Like
Save
Share
Report

In many competitive programming problems, we need to find greatest common divisor also known as gcd. Euclids algorithm to find gcd has been discussed here.
C++ has the built-in function for calculating GCD. This function is present in header file. 
Syntax for C++14 :

 Library: 'algorithm'
 __gcd(m, n) 
Parameter :  m, n
Return Value :  0 if both m and n are zero, 
else gcd of m and n.

Syntax for C++17 :

Library: 'numeric'
gcd(m, n)
Parameter :  m, n
Return Value :  0 if both m and n are zero,
else gcd of m and n.

CPP




// CPP program to illustrate
// gcd function of C++ STL
#include <iostream>
#include <algorithm>
// #include<numeric> for C++17
 
using namespace std;
 
int main()
{
    cout << "gcd(6, 20) = " << __gcd(6, 20) << endl; // gcd(6,20) for C++17
}


Output

gcd(6, 20) = 2

Time Complexity: O(logn)
Auxiliary Space: O(1)

Program to Find the gcd of all numbers in a vector.

C++




#include<bits/stdc++.h>
#include <iostream>
#include <algorithm>
using namespace std;
int main()
{
    vector<int> numbers = { 12, 15, 18, 21, 24 };
    int ans =__gcd(numbers[0], numbers[1]);
    for (int i = 2; i < numbers.size(); i++)
    {
        ans = __gcd(ans, numbers[i]);
    }
    cout << "The GCD of the numbers in the vector is: " <<ans<<endl;
    return 0;
}


Output

The GCD of the numbers in the vector is: 3

Time Complexity: O(k*logn)
Auxiliary Space: O(k)

Note: If either M or N is not an integer type, or if either is (possibly cv-qualified) bool, the program is ill-formed. Also, If either |m| or |n| is not representable as a value of type std::common_type_t, the behavior is undefined. 
 

CPP




// CPP program to illustrate
// undefined behavior of
// gcd function of C++ STL
#include <iostream>
#include <algorithm>
// #include<numeric> for C++17
 
using namespace std;
 
int main()
{
    cout << "gcd(2.0, 8) = " << __gcd(2.0, 8) << endl; // gcd(2.0,8) for C++17
}


Output: 
Error, As the data type float is not supported by std::gcd.



Last Updated : 31 Jan, 2023
Like Article
Save Article
Previous
Next
Share your thoughts in the comments
Similar Reads