LC.100.Same Tree

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)

复制代码
 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     }
复制代码

 




posted @   davidnyc  阅读(146)  评论(0编辑  收藏  举报
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