Leetcode OJ平台上的SameTree题目用Java递归实现

原题目如下：

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.

用java递归实现，关键是想清楚递归终止条件，谢谢木易先森

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public static  boolean isSameTree(TreeNode p, TreeNode q){
        if(p == null && q == null)
            return true;
        else if(p == null || q ==null) // one of them is null
            return false;
        else if(p.val != q.val)
            return false;
        else
            return (isSameTree(p.left,q.left) && isSameTree(p.right,q.right));
    }
}