https://leetcode.com/problems/same-tree/description/
Given two binary trees, write a function to check if they are the same or not.
Two binary trees are considered the same if they are structurally identical and the nodes have the same value.
Example 1:
Input: 1 1
/ /
2 3 2 3
[1,2,3], [1,2,3]
Output: true
Example 2:
Input: 1 1
/
2 2
[1,2], [1,null,2]
Output: false
Example 3:
Input: 1 1
/ /
2 1 1 2
[1,2,1], [1,1,2]
Output: false
pre-order 第一次碰见就要“打印”（PRE） 而不是饶了一圈回来再打印（POST）
这道题要一起走
time: o(n)
space: o(n)
1 public boolean isSameTree(TreeNode p, TreeNode q) {
2 //corner cases
3 if (p == null && q ==null) return true;
4 else if(p == null&& q!=null ) return false;
5 else if (p != null && q == null) return false ;
6 /*
7 上面两句可以简化成
8 if(p == null || q == null)
9 * */
10 //先打印: 当前点不满足就直接往上面反弹 不用往下走了
11 if (p !=null && q!=null){
12 if (p.val != q.val) return false ;
13 }
14 //往下走
15 boolean leftCheck = isSameTree(p.left, q.left);
16 boolean rightCheck = isSameTree(p.right, q.right);
17 //下面的回来了，综合下 左边满足，右边也满足，当前也满足
18 return leftCheck && rightCheck && p.val ==q.val ;
19 }