Symmetric Tree (Easy)

Description

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

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For example, this binary tree is symmetric:

    1
   / \
  2   2
 / \ / \
3  4 4  3
But the following is not:
    1
   / \
  2   2
   \   \
   3    3
Note:
Bonus points if you could solve it both recursively and iteratively.

Analysis

递归遍历左右孩子节点比较即可

My Solution

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//C++
/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
private:
    bool check(TreeNode *l,TreeNode *r)
    {
        if(l==NULL || r==NULL)
            return l==r;
        if(l->val!=r->val)
            return false;
        return check(l->left,r->right) && check(l->right,r->left);
    }
public:
    bool isSymmetric(TreeNode *root) {
        if(root==NULL)
            return true;
        return this->check(root->left,root->right);
    }
};