Leetcode - 101. Symmetric Tree

https://leetcode.com/problems/symmetric-tree/

Solution 1

/**
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */
/**
 * @param {TreeNode} root
 * @return {boolean}
 */
var isSymmetric = function (root) {
  return root === null || isMirrorValue(root.left, root.right);
};

const isMirrorValue = (left, right) => {
  if (left === null && right === null) {
    return true;
  }
  if (left === null || right === null) {
    return false;
  }

  if (left.val === right.val) {
    return (
      isMirrorValue(left.right, right.left) &&
      isMirrorValue(left.left, right.right)
    );
  } else {
    return false;
  }
};