Symmetric Tree.cpp

/*
Symmetric Tree
==============

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;

    queue<TreeNode *> q;
    q.push(root);
    q.push(root);

    while (q.size())
    {
      auto one = q.front();
      q.pop();
      auto two = q.front();
      q.pop();

      if (!one && !two)
        continue;
      if (!one || !two)
        return false;
      if (one->val != two->val)
        return false;
      q.push(one->left);
      q.push(two->right);
      q.push(one->right);
      q.push(two->left);
    }
    return true;
  }
};