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;
    }
};