Same Tree

Problem:
Given two binary trees, write a function to check if they are equal or not.
Two binary trees are considered equal if they are structurally identical and the nodes have the same value.

Solution:
/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    bool isSameTree(TreeNode *p, TreeNode *q) {
        if (p == NULL && q == NULL)
            return true;
        else if (p != NULL && q != NULL)
            return p -> val == q -> val &&
                isSameTree(p -> left, q -> left) &&
                isSameTree(p -> right, q -> right);
        else
            return false;
    }
};