My code is showing 'true' as output instead of 'False' - c++

Question

So there is a question in Leetcode in which we need to tell whether two binary trees are identical or not. So my function is working correctly for the inputs [1,2,3] and [1,2,3]
but it is printing 'true' for the inputs [1,2] and [1,NULL,2] instead of printing 'false'. Please can anyone tell me what have i done wrong in this program.
/**
* 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) {}
* enter code here TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
* };
*/
class Solution
{
public:
bool isSameTree(TreeNode *p, TreeNode *q)
{
if (p == NULL && q == NULL)
return true;
if (p != NULL && q != NULL)
{
if (p->val != q->val)
return false;
else
{
isSameTree(p->left, q->left);
isSameTree(p->right, q->right);
}
return true;
}
else
return false;
}
};

Answer 1

You're completely ignoring the results of those recursive calls. The point using recursion here is that two trees are the same if:
Their values are the same AND
Their respective children are the same.
You're testing the former, but never reaping the results of the latter. In reality, what you really should be trying to do is this:
class Solution
{
public:
bool isSameTree(const TreeNode *p, const TreeNode *q)
{
if (p == q) // same actual tree or both NULL
return true;
if (p != NULL && q != NULL)
{
return p->val == q->val &&
isSameTree(p->left, q->left) &&
isSameTree(p->right, q->right);
}
return false;
}
};