FilesExpand file tree

master

/

test09.java

Copy path

Blame

More file actions

Blame

More file actions

Latest commit

 

History

History

History

67 lines (61 loc) · 1.81 KB

master

/

test09.java

Copy path

Top

File metadata and controls

• Code
• Blame

67 lines (61 loc) · 1.81 KB

Raw

Copy raw file

Download raw file

Open symbols panel

Edit and raw actions

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

53

54

55

56

57

58

59

60

61

62

63

64

65

66

67

package byteDance;

import java.util.ArrayList;

import java.util.LinkedList;

import java.util.List;

import java.util.Queue;

/**

* Created by lizeyang on 2020/5/12.

* 从上往下打印二叉树

*/

class TreeNode {

int val;

TreeNode left;

TreeNode right;

TreeNode(int val) {

this.val = val;

}

}

public class test09 {

//利用队列实现层次遍历，时间复杂度O(n)，空间复杂度O(n)

public static List<List<Integer>> test(TreeNode root) {

List<List<Integer>> res = new ArrayList<>();

if (root == null) {

return res;

}

Queue<TreeNode> queue = new LinkedList<>();

queue.offer(root);

int level = 0;

while (!queue.isEmpty()) {

int size = queue.size();

res.add(new ArrayList<>());

for (int i = 0; i < size; i++) {

TreeNode node = queue.poll();

res.get(level).add(node.val);

if (node.left != null) {

queue.offer(node.left);

}

if (node.right != null) {

queue.offer(node.right);

}

}

level++;

}

return res;

}

public static void main(String[] args) {

TreeNode root = new TreeNode(5);

root.left = new TreeNode(4);

root.right = new TreeNode(8);

root.left.left = new TreeNode(3);

root.right.left = new TreeNode(7);

root.right.left.left = new TreeNode(6);

root.right.right = new TreeNode(9);

List<List<Integer>> res = test(root);

for (int i = 0; i < res.size(); i++) {

for (int j = 0; j < res.get(i).size(); j++) {

System.out.print(res.get(i).get(j) + " ");

}

System.out.println();

}

}

}