[leetcode]Symmetric Tree

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

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.

 

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    bool sym(TreeNode *root1, TreeNode *root2){
        if(!root1 && !root2) return true;
        if(!root1 || !root2) return false;
        
        if(root1->val != root2->val) return false;
        
        if(!sym(root1->left,root2->right)) return false;
        if(!sym(root1->right,root2->left)) return false;

        return true;
        
    }

    bool isSymmetric(TreeNode *root) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if(!root) return true;
        return sym(root->left, root->right);
    }
};