GCD-sum.js

/* Given the sum and gcd of two numbers, return those two numbers in ascending order. If the numbers do not exist, return -1, (or NULL in C, tuple (-1,-1) in C#, pair (-1,-1) in C++,None in Rust, array {-1,-1}  in Java and Golang).

For example: 
Given sum = 12 and gcd = 4...

solve(12,4) = [4,8]. The two numbers 4 and 8 sum to 12 and have a gcd of 4.

solve(12,5) = -1. No two numbers exist that sum to 12 and have gcd of 5.

solve(10,2) = [2,8]. Note that [4,6] is also a possibility but we pick the one with the lower first element: 2 < 4, so we take [2,8].
More examples in test cases.

Good luck!

*/

//solution

function solve(x, y) {
    return x % y ? -1 : [y, x - y];
  }