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# Q100. Same Tree

直达：<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
```

## 分析

两棵树相等的充要条件是根节点内容相同且左右两棵字数都是相同的树

## C++代码

```cpp
/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    bool 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;
        else return isSameTree(p->left, q->left) && isSameTree(p->right, q->right);
    }
};
```