LeetCode:Symmetric Tree

Symmetric Tree

Total Accepted: 80764  Total Submissions: 249396  Difficulty: Easy

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.

confused what "{1,#,2,3}" means? > read more on how binary tree is serialized on OJ.

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code:

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