Same Tree 比较两个二叉树是否完全相同

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.

给定两个二叉树，判断是否完全相同。

若两个二叉树完全相同，则每个节点的左子树和右子树必然都相同。

可以采用递归方式，从根节点开始：

 1 /**
 2  * Definition for binary tree
 3  * struct TreeNode {
 4  *     int val;
 5  *     TreeNode *left;
 6  *     TreeNode *right;
 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 8  * };
 9  */
10 class Solution {
11 public:
12     bool isSameTree(TreeNode *p, TreeNode *q) {
13         if(p == NULL && q == NULL)
14             return true;
15         else if(p == NULL || q == NULL)
16             return false;
17         
18         if(p->val != q->val)
19             return false;
20         
21         bool left = isSameTree(p->left,q->left);
22         bool right = isSameTree(p->right,q->right);
23         
24         return left && right;
25     }
26 };