# 101. Symmetric Tree

**<font color=red>难度Easy<font>**

## 刷题内容
> 原题连接

* https://leetcode.com/problems/symmetric-tree/

> 内容描述

```
Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center).

For example, this binary tree [1,2,2,3,4,4,3] is symmetric:

    1
   / \
  2   2
 / \ / \
3  4 4  3
But the following [1,2,2,null,3,null,3] is not:
    1
   / \
  2   2
   \   \
   3    3
```

可以直接DFS比较左右两颗子树是否相等，若想等返回true，若不等，返回false
> 思路
******- 时间复杂度: O(N)******- 空间复杂度: O(1)******

```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 judge(TreeNode* oTree,TreeNode* mTree){
        if((oTree != nullptr) && (mTree != nullptr))
        {
            if((oTree ->val == mTree  ->val) && (oTree ->val == mTree ->val))
                return judge(oTree ->left,mTree ->right) && judge(oTree ->right,mTree ->left);
                return false;
        }
        if(oTree == mTree)
            return true;
        return false;
    }
    bool isSymmetric(TreeNode* root) {
      if(root != nullptr)
        return judge(root ->left,root ->right);
    return true;
    }
};
```