same-tree

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.

/**
 * 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;  
     if(p==NULL&&q!=NULL)  
        return false;  
     if(p!=NULL&&q==NULL)  
        return false;  
     if(p!=NULL&&q!=NULL&&p->val!=q->val)  
        return false;    
        return (isSameTree(p->left,q->left))&&(isSameTree(p->right,q->right));  
    }  
};