Same Tree

/**
* Definition for a binary tree node.
* 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;
if(p == NULL && q != NULL)
return false;
if(p != NULL && q == NULL)
return false;

//establish a recursive relation
if(p->val != q->val)
return false;
return isSameTree(p->left, q->left) && isSameTree(p->right, q->right);
}
};