2543-check-if-point-is-reachable.js

/**
 * 2543. Check if Point Is Reachable
 * https://leetcode.com/problems/check-if-point-is-reachable/
 * Difficulty: Hard
 *
 * There exists an infinitely large grid. You are currently at point (1, 1), and you need
 * to reach the point (targetX, targetY) using a finite number of steps.
 *
 * In one step, you can move from point (x, y) to any one of the following points:
 * - (x, y - x)
 * - (x - y, y)
 * - (2 * x, y)
 * - (x, 2 * y)
 *
 * Given two integers targetX and targetY representing the X-coordinate and Y-coordinate of
 * your final position, return true if you can reach the point from (1, 1) using some number
 * of steps, and false otherwise.
 */

/**
 * @param {number} targetX
 * @param {number} targetY
 * @return {boolean}
 */
var isReachable = function(targetX, targetY) {
  let g = gcd(targetX, targetY);
  while (g % 2 === 0) {
    g /= 2;
  }

  return g === 1;
};

function gcd(a, b) {
  while (b) {
    a %= b;
    [a, b] = [b, a];
  }
  return a;
}