LeetCode 100. Same Tree（相同的树）

原题网址：https://leetcode.com/problems/same-tree/

Given two binary trees, write a function to check if they are equal or not.

Two binary trees are considered equal if they are structurally identical and the nodes have the same value.
方法：自顶向下，递归。

/**
* Definition for a binary tree node.
* public class TreeNode {
*     int val;
*     TreeNode left;
*     TreeNode right;
*     TreeNode(int x) { val = x; }
* }
*/
public class Solution {
public boolean isSameTree(TreeNode p, TreeNode q) {
if (p == null && q == null) return true;
if (p == null || q == null) return false;
if (p.val != q.val) return false;
if (p.left != null || q.left != null) {
if (p.left == null || q.left == null) return false;
if (!isSameTree(p.left, q.left)) return false;
}
if (p.right != null || q.right != null) {
if (p.right == null || q.right == null) return false;
if (!isSameTree(p.right, q.right)) return false;
}
return true;
}
}