Leetcode 101 Symmetric Tree

    1
   / \
  2   2
 / \ / \
3  4 4  3

    1
   / \
  2   2
   \   \
   3    3

/**
 * 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 dfs(TreeNode* t1,TreeNode* t2)
    {
        if(!t1 || !t2)
        {
            if(!t1 && !t2) return true;
            return false;
        }
        if(t1->val!=t2->val) return false;
        return dfs(t1->left,t2->right) && dfs(t1->right,t2->left);
    }
    bool isSymmetric(TreeNode* root) 
    {
        if(!root) return true;
        return dfs(root->left,root->right);
    }
};