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：

 /**
  * 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;
         else if(p == NULL || q == NULL)
             return false;

         if(p->val != q->val)
             return false;

         bool left = isSameTree(p->left,q->left);
         bool right = isSameTree(p->right,q->right);

         return left && right;
     }
 };