index.js

/*
 * @lc app=leetcode id=101 lang=javascript
 *
 * [101] Symmetric Tree
 *
 * https://leetcode.com/problems/symmetric-tree/description/
 *
 * algorithms
 * Easy (42.50%)
 * Total Accepted:    588.6K
 * Total Submissions: 1.3M
 * Testcase Example:  '[1,2,2,3,4,4,3]'
 *
 * Given a binary tree, check whether it is a mirror of itself (ie, symmetric
 * around its center).
 * 
 * For example, this binary tree [1,2,2,3,4,4,3] is symmetric:
 * 
 * 
 * ⁠   1
 * ⁠  / \
 * ⁠ 2   2
 * ⁠/ \ / \
 * 3  4 4  3
 * 
 * 
 * 
 * 
 * But the following [1,2,2,null,3,null,3] is not:
 * 
 * 
 * ⁠   1
 * ⁠  / \
 * ⁠ 2   2
 * ⁠  \   \
 * ⁠  3    3
 * 
 * 
 * 
 * 
 * Follow up: Solve it both recursively and iteratively.
 * 
 */
/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} root
 * @return {boolean}
 */
var isSymmetric = function(root) {
    const isSymmetricHelp = (root1, root2) => {
        if (!root1 && !root2) return true;
        if (!root1 || !root2) return false;
        if (root1.val !== root2.val) return false;
        return isSymmetricHelp(root1.left, root2.right) && isSymmetricHelp(root1.right, root2.left)
    };
    return isSymmetricHelp(root, root)
};

module.exports = {
    id:'101',
    title:'Symmetric Tree',
    url:'https://leetcode.com/problems/symmetric-tree/description/',
    difficulty:'Easy',
}