Greatest Common Divisor from a set of more than 2 integers

Question

There are several questions on Stack Overflow discussing how to find the Greatest Common Divisor of two values. One good answer shows a neat recursive function

Answer 1

Without using LINQ.

    static int GCD(int a, int b)
    {
        if (b == 0) return a;
        return GCD(b, a % b);
    }

    static int GCD(params int[] numbers)
    {
        int gcd = 0;
        int a = numbers[0];
        for(int i = 1; i < numbers.Length; i++)
        {
            gcd = GCD(a, numbers[i]);
            a = numbers[i];
        }

        return gcd;
    }

Answer 2

And here you have code example using LINQ and GCD method from question you linked. It is using theoretical algorithm described in other answers ... GCD(a, b, c) = GCD(GCD(a, b), c)

static int GCD(int[] numbers)
{
    return numbers.Aggregate(GCD);
}

static int GCD(int a, int b)
{
    return b == 0 ? a : GCD(b, a % b);
}

Answer 3

By using this, you can pass multiple values as well in the form of array:-

// pass all the values in array and call findGCD function
    int findGCD(int arr[], int n) 
    { 
        int gcd = arr[0]; 
        for (int i = 1; i < n; i++) {
            gcd = getGcd(arr[i], gcd); 
}

        return gcd; 
    } 

// check for gcd
int getGcd(int x, int y) 
    { 
        if (x == 0) 
            return y; 
        return gcd(y % x, x); 
    } 

Answer 4

You could use this common property of a GCD:

GCD(a, b, c) = GCD(a, GCD(b, c)) = GCD(GCD(a, b), c) = GCD(GCD(a, c), b)

Assuming you have GCD(a, b) already defined it is easy to generalize:

public class Program
{
    static void Main()
    {
        Console.WriteLine(GCD(new[] { 10, 15, 30, 45 }));
    }

    static int GCD(int a, int b)
    {
        return b == 0 ? a : GCD(b, a % b);
    }

    static int GCD(int[] integerSet)
    {
        return integerSet.Aggregate(GCD);
    }    
}

Answer 5

GCD(a, b, c) = GCD(a, GCD(b, c)) = GCD(GCD(a, b), c) = GCD(GCD(a, c), b)

enter code here

public class Program { static void Main() { Console.WriteLine(GCD(new[] { 10, 15, 30, 45 })); } static int GCD(int a, int b) { return b == 0 ? a : GCD(b, a % b); } static int GCD(int[] integerSet) { return integerSet.Aggregate(GCD); } }

Answer 6

Rewriting this as a single function...

    static int GCD(params int[] numbers)
    {
        Func<int, int, int> gcd = null;
        gcd = (a, b) => (b == 0 ? a : gcd(b, a % b));
        return numbers.Aggregate(gcd);
    }