Same Tree

Analysis:
Use recursion.

Solution:

 /**  
  * 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;  
    if (p == null && q != null) return false;  
    if (p != null && q == null) return false;  
    return isSameTree(p.left, q.left) && isSameTree(p.right, q.right) && p.val == q.val;  
   }  
 }