[Leetcode]100. Same Tree -David_Lin

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.

思路：同时递归两棵树，如果节点值不相等或者一棵树已经递归到头了而另一棵还没有，返回false;

 /**
  * Definition for a binary tree node.
  * public class TreeNode {
  *     int val;
  *     TreeNode left;
  *     TreeNode right;
  *     TreeNode(int x) { val = x; }
  * }
  */
 class Solution {
     public boolean isSameTree(TreeNode p, TreeNode q) {
         if (p==null&&q==null)
             return true;                 //一开始如果传进两颗空树，返回true
         if ((p==null&&q!=null)||(p!=null&&q==null))
             return false;                //递归过程中，一棵树递归到头了，而另一颗没有
         if (p.val!=q.val)
             return false;
         return isSameTree(p.left,q.left)&&isSameTree(p.right,q.right);
                                               // 同时递归
     }
 }