[LeetCode]101. Symmetric Tree

101. Symmetric Tree

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

For example, this binary tree [1,2,2,3,4,4,3] is symmetric:

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

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/** * 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 isSymmetric(root, root);    }    bool isSymmetric(TreeNode* root1, TreeNode* root2){        if(root1 == NULL && root2 == NULL)            return true;        if(root1 == NULL || root2 == NULL)            return false;        if(root1->val != root2->val)            return false;        return isSymmetric(root1->left, root2->right) && isSymmetric(root1->right, root2->left);    }};