-
Notifications
You must be signed in to change notification settings - Fork 1
Expand file tree
/
Copy pathBinaryTreeLevelOrderTraversal2.java
More file actions
49 lines (36 loc) · 1.51 KB
/
Copy pathBinaryTreeLevelOrderTraversal2.java
File metadata and controls
49 lines (36 loc) · 1.51 KB
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
// Given a binary tree, return the bottom-up level order traversal of
// its nodes' values. (ie, from left to right, level by level from leaf to root).
// See: https://leetcode.com/problems/binary-tree-level-order-traversal-ii/
package leetcode.tree;
import static leetcode.util.tree.BinTreeUtil.initTree;
import java.util.ArrayList;
import java.util.Collections;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import leetcode.util.tree.TreeNode;
public class BinaryTreeLevelOrderTraversal2 {
public List<List<Integer>> levelOrderBottom(TreeNode root) {
Map<Integer, List<Integer>> resMap = new LinkedHashMap<Integer, List<Integer>>();
dfs(root, 0, resMap);
List<List<Integer>> res = new ArrayList<>(resMap.values());
Collections.reverse(res);
return res;
}
private void dfs(TreeNode root, int level, Map<Integer, List<Integer>> resultMap) {
if (root == null)
return;
if (!resultMap.containsKey(level)) {
resultMap.put(level, new ArrayList<>());
}
resultMap.get(level).add(root.val);
dfs(root.left, level + 1, resultMap);
dfs(root.right, level + 1, resultMap);
}
public static void main(String[] args) {
BinaryTreeLevelOrderTraversal2 sln = new BinaryTreeLevelOrderTraversal2();
TreeNode t1 = initTree(3, 9, 20, null, null, 15, 7);
System.out.println(sln.levelOrderBottom(t1));
System.out.println(sln.levelOrderBottom(null));
}
}