leetcode-- 100. Same Tree

1、问题描述

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.

2、边界条件：无

3、思路：递归，两颗数is same的条件是val相等，子树也是same。但是判断val的前提条件是有val，即不为null。

base case：两颗数都为空；一颗为空，一颗不为空。

4、代码实现

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public boolean isSameTree(TreeNode p, TreeNode q) {
        if (p == null && q == null) {//base case是两个节点都为空
            return true;
        }
        if (p == null || q == null) {
            return false;
        }
        return p.val == q.val
               && isSameTree(p.left, q.left)
               && isSameTree(p.right, q.right);
    }
}