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

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/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} root
 * @return {boolean}
 */
const isSymmetric = (root) => {
    return !root || judgeSymmetric(root.left, root.right)
}

const judgeSymmetric = (left, right) => {
    if (!left && !right) {
        return true
    }
    if (!left || !right) {
        return false
    }
    return left.val === right.val && judgeSymmetric(left.left, right.right) && judgeSymmetric(left.right, right.left)
}