LeetCode-in-Cpp
101. Symmetric Tree
Easy
Given the root of a binary tree, check whether it is a mirror of itself (i.e., symmetric around its center).
Example 1:
Input: root = [1,2,2,3,4,4,3]
Output: true
Example 2:
Input: root = [1,2,2,null,3,null,3]
Output: false
Constraints:
- The number of nodes in the tree is in the range
[1, 1000]. -100 <= Node.val <= 100
Follow up: Could you solve it both recursively and iteratively?
Solution
/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode() : val(0), left(nullptr), right(nullptr) {}
* TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
* TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
* };
*/
class Solution {
public:
bool isSymmetric(TreeNode* root) {
if (root == nullptr) {
return true;
}
return helper(root->left, root->right);
}
private:
bool helper(TreeNode* leftNode, TreeNode* rightNode) {
if (leftNode == nullptr || rightNode == nullptr) {
return leftNode == nullptr && rightNode == nullptr;
}
if (leftNode->val != rightNode->val) {
return false;
}
return helper(leftNode->left, rightNode->right) && helper(leftNode->right, rightNode->left);
}
};