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std::lcm

From cppreference.com
< cpp‎ | numeric
Defined in header <numeric>
template< class M, class N >
constexpr std::common_type_t<M, N> lcm( M m, N n );
(since C++17)

Computes the least common multiple of the integers m and n.

Contents

[edit] Parameters

m, n - integer values

[edit] Return value

If either m or n is zero, returns zero. Otherwise, returns the least common multiple of |m| and |n|.

[edit] Remarks

If either M or N is not an integer type, or if either is (possibly cv-qualified) bool, the program is ill-formed.

The behavior is undefined if |m|, |n|, or the least common multiple of |m| and |n| is not representable as a value of type std::common_type_t<M, N>.

[edit] Exceptions

Throws no exceptions.

[edit] Notes

Feature testing macro: __cpp_lib_gcd_lcm

[edit] Example

#include <numeric>
#include <iostream>
 
#define OUT(...) std::cout << #__VA_ARGS__ << " = " << __VA_ARGS__ << '\n'
 
constexpr auto lcm(auto x, auto y) {
    return std::lcm(x,y);
}
constexpr auto lcm(auto head, auto...tail) {
    return std::lcm(head, lcm(tail...));
}
 
int main() {
    constexpr int p {2 * 2 * 3};
    constexpr int q {2 * 3 * 3};
    static_assert(2 * 2 * 3 * 3 == std::lcm(p, q));
    static_assert(225 == std::lcm(45, 75));
 
    OUT(lcm(2*3, 3*4, 4*5));
    OUT(lcm(2*3*4, 3*4*5, 4*5*6));
    OUT(lcm(2*3*4, 3*4*5, 4*5*6, 5*6*7));
}

Output:

lcm(2*3, 3*4, 4*5) = 60
lcm(2*3*4, 3*4*5, 4*5*6) = 120
lcm(2*3*4, 3*4*5, 4*5*6, 5*6*7) = 840

[edit] See also

(C++17)
constexpr function template returning the greatest common divisor of two integers
(function template) [edit]