C++ algorithm to calculate least common multiple for multiple numbers

Question

Is there a C++ algorithm to calculate the least common multiple for multiple numbers, like lcm(3,6,12) or lcm(5,7,9,12)?

Answer 1

Using the fact that lcm should be divisible by all the numbers in list. Here the list is a vector containing numbers

        int lcm=*(len.begin());
    int ini=lcm;
    int val;
    int i=1;
    for(it=len.begin()+1;it!=len.end();it++)
    {
        val=*it;
        while(lcm%(val)!=0)
        {
            lcm+=ini;
        }
        ini=lcm;
    }
    printf("%llu\n",lcm);
    len.clear();

Answer 2

I found this while searching a similar problem and wanted to contribute what I came up with for two numbers.

#include <iostream>
#include <algorithm>
using namespace std;

int main()
{
    cin >> x >> y;

    // zero is not a common multiple so error out
    if (x * y == 0)
        return -1;

    int n = min(x, y);
    while (max(x, y) % n)
        n--;

    cout << n << endl;
}

Answer 3

#include
#include

void main()
{
    clrscr();

    int x,y,gcd=1;

    cout<>x;

    cout<>y;

    for(int i=1;i<1000;++i)
    {
        if((x%i==0)&&(y%i==0))
        gcd=i;
    }

    cout<<"\n\n\nGCD :"<
    cout<<"\n\n\nLCM :"<<(x*y)/gcd;

    getch();
}

Answer 4

As of C++17, you can use std::lcm.

And here is a little program that shows how to specialize it for multiple parameters

#include <numeric>
#include <iostream>

namespace math {

    template <typename M, typename N>
    constexpr auto lcm(const M& m, const N& n) {
        return std::lcm(m, n);
    }

    template <typename M, typename ...Rest>
    constexpr auto lcm(const M& first, const Rest&... rest) {
        return std::lcm(first, lcm(rest...));
    }
}

auto main() -> int {
    std::cout << math::lcm(3, 6, 12, 36) << std::endl;
    return 0;
}

See it in action here: https://wandbox.org/permlink/25jVinGytpvPaS4v

Answer 5

boost provides functions for calculation lcm of 2 numbers (see here)

Then using the fact that

lcm(a,b,c) = lcm(lcm(a,b),c)

You can easily calculate lcm for multiple numbers as well

Answer 6

Not built in to the standard library. You need to either build it yourself or get a library that did it. I bet Boost has one...