# LeetCode 100. Same Tree 等价二叉树

## Description

https://leetcode.com/problems/same-tree/description/

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```

## Explanation

1. 当p和q都为null时候
2. 当p和q都不为null， p和q的值相等，并且p和q的左右子树都相同

## Java Solution

```/**
* 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) {
return true;
}

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

return false;
}
}```