1. /**
    2.  * Definition for a binary tree node.
    3.  * function TreeNode(val, left, right) {
    4.  *     this.val = (val===undefined ? 0 : val)
    5.  *     this.left = (left===undefined ? null : left)
    6.  *     this.right = (right===undefined ? null : right)
    7.  * }
    8.  */
    9. /**
    10.  * @param {TreeNode} root
    11.  * @param {TreeNode} subRoot
    12.  * @return {boolean}
    13.  */
    15. const isSametree = (root, subRoot) => {
    16.     if (root == null && subRoot == null) return true
    18.     //  如果有一棵树为 null, 另一棵树后面还有节点，则不符合题意
    19.     if (root === null || subRoot === null) return false
    21.     // 判断 先序遍历 的顺序是否一致
    22.     if (root.val !== subRoot.val) return false
    24.     return isSametree(root.left, subRoot.left) && isSametree(root.right, subRoot.right)
    25. }
    27. var isSubtree = function (root, subRoot) {
    28.     if (!root) return false
    30.     isSametree(root, subRoot)
    32.     // 递归遍历 root 判断是否有子树
    33.     return isSametree(root, subRoot) || isSubtree(root.left, subRoot) || isSubtree(root.right, subRoot)
    34. };