LCM of an Array

Problem

The first line has n. The second line has n positive integers. Print the least common multiple of all of them. The answer is smaller than 2^53 in all tests.

Constraints

  • 1 <= n <= 10^5
  • The answer < 2^53

Examples

Input

2
4 6

Output

12

Solutions

Best approachTime O(n log max)Space O(1)

We use lcm(x, y) = x / gcd(x, y) * y and fold the array. Dividing before multiplying avoids overflow.

Same code works in Java810172125Basic features only, so nothing changes between versions.
/*
 * Problem : Find the lcm of many numbers.
 * Input   : n, then n integers.
 * Output  : The lcm.
 * Approach: lcm(x, y) = x / gcd(x, y) * y.
 * Time    : O(n log max)
 * Space   : O(1)
 * Java    : 8 or newer.
 */
import java.util.Scanner;

public class Main {
    // This method solves the task. It receives the input and returns the answer.
    static long solve(int[] a) {
        // Step 1: The lcm of one number is the number itself.
        long result = a[0];

        // Step 2: Combine with each next number: lcm(x, y) = x / gcd(x, y) * y.
        for (int i = 1; i < a.length; i++) {
            long x = result;
            long y = a[i];
            while (y != 0) {
                long remainder = x % y;
                x = y;
                y = remainder;
            }
            // Step 3: Now x is the gcd. Divide first, then multiply, to keep the number small.
            result = result / x * a[i];
        }
        return result;
    }

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int size = scanner.nextInt();
        int[] a = new int[size];
        for (int i = 0; i < size; i++) {
            a[i] = scanner.nextInt();
        }
        System.out.println(solve(a));
    }
}
Hints (1)
  1. How are gcd and lcm related?