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Symmetric Tree

Problem statement​

Given the root of a binary tree, check whether it is a mirror of itself (i.e., symmetric around its center).

Example 1:

Input: root = [1,2,2,3,4,4,3]Output: true

Example 2:

Input: root = [1,2,2,null,3,null,3]Output: false

Constraints:

  • The number of nodes in the tree is in the range [1, 1000].
  • -100 <= Node.val <= 100
Follow up: Could you solve it both recursively and iteratively?

My solution​

/**
 * 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) {
    function traverse(left, right) {
        if (!left && !right) {
            return true
        }
        
        if (!left || !right || left.val !== right.val) {
            return false
        }
        
        return traverse(left.left, right.right) && traverse(right.left, left.right)
    }
    
    return traverse(root.left, root.right)
};