101-recursive.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 isSymmetric(TreeNode* root) {
        if(root==NULL)  return true;
        
        return isSymmetric(root->left, root->right);
    }
    
    bool isSymmetric(TreeNode *t1, TreeNode *t2){
        if(t1==NULL && t2==NULL)    return true;
        if(t1==NULL || t2==NULL)    return false;
        if(t1->val == t2->val){
            return isSymmetric(t1->left, t2->right) && isSymmetric(t1->right, t2->left);
        }else{
            return false;
        }
    }
};