same-tree

题目：

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.

程序：

class Solution {public:    bool isSameTree(TreeNode *p, TreeNode *q) {        if(p == NULL && q == NULL)            return true;        else if(p == NULL || q == NULL)            return false;        else if(p->val == q->val)            return isSameTree(p->left,q->left) && isSameTree(p->right,q->right);        return false;    }};