lintcode/leetcode由易至难第11题：Same Tree

Problem:

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.
Code:

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

Code2:

public boolean isSameTree(TreeNode p, TreeNode q) {
if(p == null && q == null) return true;
if(p == null || q == null) return false; //第一个if已经排除掉左右都为true了
if(p.val == q.val)
return isSameTree(p.left, q.left) && isSameTree(p.right, q.right);
return false; //此处可以省略else
}