-
Notifications
You must be signed in to change notification settings - Fork 0
/
MergeTwoBinaryTrees.java
52 lines (48 loc) · 1.5 KB
/
MergeTwoBinaryTrees.java
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
package easy;
/**
* Given two binary trees and imagine that when you put one of them to cover the other, some nodes of the two trees are overlapped while
* the others are not.
* You need to merge them into a new binary tree. The merge rule is that if two nodes overlap, then sum node values up as the new value
* of the merged node. Otherwise, the NOT null node will be used as the node of new tree.
*
* Example 1:
* Input:
* Tree 1 Tree 2
* 1 2
* / \ / \
* 3 2 1 3
* / \ \
* 5 4 7
* Output:
* Merged tree:
* 3
* / \
* 4 5
* / \ \
* 5 4 7
*
* 解决思路:
* 二叉树合并,经典DFS问题
* 边界检查为都等于空 返回空, 其中一方为空 返回另一边
* 让左边的值等于左边加右边
* 递归调用, 返回左边
*
* Created by second on 2017/9/8.
*/
public class MergeTwoBinaryTrees {
public TreeNode mergeTrees(TreeNode t1, TreeNode t2) {
if (t1 == null && t2 == null) return null;
if (t1 == null) return t2;
if (t2 == null) return t1;
t1.val += t2.val;
t1.left = mergeTrees(t1.left, t2.left);
t1.right = mergeTrees(t1.right, t2.right);
return t1;
}
private class TreeNode {
int val;
TreeNode left;
TreeNode right;
TreeNode(int x) { val = x; }
}
}