Same Tree

废话不多说。直接上代码，哈哈，痛快：

/**
 * 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);
    }
};