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101.symmetric-tree.cpp
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66 lines (59 loc) · 1.47 KB
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// Tag: Tree, Depth-First Search, Breadth-First Search, Binary Tree
// Time: O(N)
// Space: O(H)
// Ref: -
// Note: -
// 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?
/**
* 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) {
return true;
}
return helper(root->left, root->right);
}
bool helper(TreeNode* left, TreeNode* right) {
if (!left && !right) {
return true;
}
if (!left or !right) {
return false;
}
if (left->val != right->val) {
return false;
}
return helper(left->left, right->right) && helper(left->right, right->left);
}
};