100. Same Tree

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

Two binary trees are considered the same if they are structurally identical and the nodes have the same value.

Example 1:
Input:     1         1
          / \       / \
         2   3     2   3

        [1,2,3],   [1,2,3]

Output: true

Example 2:
Input:     1         1
          /           \
         2             2

        [1,2],     [1,null,2]

Output: false

Example 3:
Input:     1         1
          / \       / \
         2   1     1   2

        [1,2,1],   [1,1,2]

Output: false

难度：easy

题目：
给定两二叉树，写函数检查它们是否相同。
两个二叉树是否相同是由其结构和值都相同来决定。

思路：递归

/**
 * 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 (null == p && null != q || null != p && null == q) {
            return false;
        }
        
        if (null == p && null == q) {
            return true;
        }
        
        if (p.val != q.val) {
            return false;
        }
        
        return isSameTree(p.left, q.left) && isSameTree(p.right, q.right);
    }
}