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} p
    11.  * @param {TreeNode} q
    12.  * @return {boolean}
    13.  */
    14. var isSameTree = function(p, q) {
    15.   if(q === null && p === null) {
    16.     return true
    17.   }
    19.   if(q === null ||  p === null) {
    20.     return false
    21.   }
    23.   return p.val === q.val && isSameTree(q.left, p.left) && isSameTree(q.right, p.right)
    24. };