Q5_symmetric_tree.cpp

// 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

#include<bits/stdc++.h>
using namespace std;

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 {
private:
    bool checkSymmetric(TreeNode* root1, TreeNode* root2) {
        if(!root1 && !root2) return true;
        if(!root1 || !root2) return false;

        bool left = checkSymmetric(root1->left, root2->right);
        bool right = checkSymmetric(root1->right, root2->left);

        return root1->val == root2->val && left && right;
    }
public:
    bool isSymmetric(TreeNode* root) {
        return checkSymmetric(root->left, root->right);
    }
};

// Time Complexity  : O(n) 
// Space Complexity : O(min height of tree)