101 Symmetric Tree¶
Problem 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:
But the following [1,2,2,null,3,null,3] is not:
Note: Bonus points if you could solve it both recursively and iteratively.
Solution: Recursion¶
Time complexity: O(n) Space complexity: O(n)
class Solution {
public:
bool isSymmetric(TreeNode* root) {
return isMirror(root, root);
}
private:
bool isMirror(TreeNode* root1, TreeNode* root2) {
if (!root1 && !root2) return true;
if (!root1 || !root2) return false;
return root1->val == root2->val
&& isMirror(root1->right, root2->left)
&& isMirror(root1->left, root2->right);
}
};