[Easy - wk4 - Q2] 101. Symmetric Tree

class Solution {
    bool helper(TreeNode *left, TreeNode *right) {
        if (!left && !right) return true;
        if (!left || !right) return false;
        return left->val == right->val &&
               helper(left->left, right->right) &&
               helper(left->right, right->left);
    }
    
public:
    bool isSymmetric(TreeNode *root) {
        return helper(root, root);
    }
};

var isSymmetric = function(root) {
  if (root === null) {
    return true;
  }

  return isMirror(root.left, root.right);
}
var isMirror = function(tree1, tree2) {
  if (tree1 === null || tree2 === null) {
    return tree1 === tree2;
  }

  if (tree1.val !== tree2.val) {
    return false;
  }

  return isMirror(tree1.left, tree2.right) && isMirror(tree1.right, tree2.left);
};