https://github.com/emahtab/binary-tree-level-order-traversal-ii
Binary Tree Level Order Traversal
https://github.com/emahtab/binary-tree-level-order-traversal-ii
bfs binary-tree binary-tree-traversal leetcode problem-solving
Last synced: 8 months ago
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Binary Tree Level Order Traversal
- Host: GitHub
- URL: https://github.com/emahtab/binary-tree-level-order-traversal-ii
- Owner: eMahtab
- Created: 2020-05-12T10:05:25.000Z (over 5 years ago)
- Default Branch: master
- Last Pushed: 2020-05-12T10:11:14.000Z (over 5 years ago)
- Last Synced: 2025-02-02T03:26:16.862Z (10 months ago)
- Topics: bfs, binary-tree, binary-tree-traversal, leetcode, problem-solving
- Homepage:
- Size: 3.91 KB
- Stars: 1
- Watchers: 1
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
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README
# Binary Tree Level Order Traversal II
## https://leetcode.com/problems/binary-tree-level-order-traversal-ii
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).
```
For example:
Given binary tree [3,9,20,null,null,15,7],
3
/ \
9 20
/ \
15 7
return its bottom-up level order traversal as:
[
[15,7],
[9,20],
[3]
]
```
# Implementation 1 :
```java
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode() {}
* TreeNode(int val) { this.val = val; }
* TreeNode(int val, TreeNode left, TreeNode right) {
* this.val = val;
* this.left = left;
* this.right = right;
* }
* }
*/
class Solution {
public List> levelOrderBottom(TreeNode root) {
List> res = new ArrayList<>();
if(root == null)
return res;
Queue q = new LinkedList<>();
q.offer(root);
while(!q.isEmpty()) {
int size = q.size();
List level = new ArrayList<>();
for(int i = 1; i <= size; i++) {
TreeNode current = q.poll();
level.add(current.val);
if(current.left != null)
q.offer(current.left);
if(current.right != null)
q.offer(current.right);
}
res.add(level);
}
Collections.reverse(res);
return res;
}
}
```
# Implementation 2 :
```java
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
class Solution {
public List> levelOrderBottom(TreeNode root) {
List> result = new ArrayList>();
if(root == null){
return result;
}
Queue queue = new ArrayDeque();
queue.offer(root);
while(!queue.isEmpty()){
int size = queue.size();
List level = new ArrayList();
for(int i = 0; i < size; i++){
TreeNode node = queue.poll();
level.add(node.val);
if(node.left != null)
queue.offer(node.left);
if(node.right != null)
queue.offer(node.right);
}
result.add(0,level);
}
return result;
}
}
```