101. Symmetric Tree

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101. Symmetric Tree

Description

Given the root of a binary tree, check whether it is a mirror of itself (i.e., symmetric around its center).

Example 1:

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Input: root = [1,2,2,3,4,4,3]
Output: true

Example 2:

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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?

Hints/Notes

  • N/A

Solution

Language: C++

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/**
 * 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 isMirrorTree(root->left, root->right);
    }

    bool isMirrorTree(TreeNode* p, TreeNode* q) {
        if (!p && !q) {
            return true;
        }

        if (!p || !q) {
            return false;
        }

        if (p->val != q->val) {
            return false;
        }

        return isMirrorTree(p->left, q->right) &&
               isMirrorTree(p->right, q->left);
    }
};