101. Symmetric Tree.cc

//Using recursion method
//TC: O(n/2) = O(n)
//SC: O(logn)

/**
 * 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 Symmetric(TreeNode* p, TreeNode* q) {
        if (p == nullptr && q == nullptr) {
            return true;
        } else if (p == nullptr || q == nullptr) {
            return false;
        } else if (p->val != q->val) {
            return false;
        }
        
        return Symmetric(p->left, q->right) && Symmetric(p->right, q->left);
        
    }
    
    
    
    bool isSymmetric(TreeNode* root) {
        if (root == nullptr)
            return true;
        return Symmetric(root->left, root->right);
    }
};