98 lines
2.4 KiB
Java
98 lines
2.4 KiB
Java
// Source : https://oj.leetcode.com/problems/binary-tree-level-order-traversal/
|
|
// Inspired by : http://www.jiuzhang.com/solutions/binary-tree-level-order-traversal/
|
|
// Author : Lei Cao
|
|
// Date : 2015-10-08
|
|
|
|
/**********************************************************************************
|
|
*
|
|
* Given a binary tree, return the level order traversal of its nodes' values.
|
|
* (ie, from left to right, level by level).
|
|
*
|
|
* For example:
|
|
* Given binary tree {3,9,20,#,#,15,7},
|
|
*
|
|
* 3
|
|
* / \
|
|
* 9 20
|
|
* / \
|
|
* 15 7
|
|
*
|
|
* return its level order traversal as:
|
|
*
|
|
* [
|
|
* [3],
|
|
* [9,20],
|
|
* [15,7]
|
|
* ]
|
|
*
|
|
* confused what "{1,#,2,3}" means? > read more on how binary tree is serialized on OJ.
|
|
*
|
|
* OJ's Binary Tree Serialization:
|
|
*
|
|
* The serialization of a binary tree follows a level order traversal, where '#' signifies
|
|
* a path terminator where no node exists below.
|
|
*
|
|
* Here's an example:
|
|
*
|
|
* 1
|
|
* / \
|
|
* 2 3
|
|
* /
|
|
* 4
|
|
* \
|
|
* 5
|
|
*
|
|
* The above binary tree is serialized as "{1,2,3,#,#,4,#,#,5}".
|
|
*
|
|
*
|
|
**********************************************************************************/
|
|
|
|
package binaryTreeLevelOrderTraversal;
|
|
|
|
import java.util.ArrayList;
|
|
import java.util.LinkedList;
|
|
import java.util.List;
|
|
import java.util.Queue;
|
|
|
|
public class binaryTreeLevelOrderTraversal {
|
|
/**
|
|
* @param root: The root of binary tree.
|
|
* @return: Level order a list of lists of integer
|
|
*/
|
|
public List<List<Integer>> levelOrder(TreeNode root) {
|
|
List<List<Integer>> results = new ArrayList<>();
|
|
if (root == null) {
|
|
return results;
|
|
}
|
|
|
|
ArrayList<Integer> values = new ArrayList<Integer>();
|
|
Queue<TreeNode> q = new LinkedList<>();
|
|
|
|
q.offer(root);
|
|
q.offer(null);
|
|
|
|
while (q.size() > 0) {
|
|
TreeNode node = q.poll();
|
|
// null node used as a separator of every level
|
|
if (node == null) {
|
|
results.add(new ArrayList<>(values));
|
|
values.clear();
|
|
if (q.size() == 0) {
|
|
break;
|
|
}
|
|
q.offer(null);
|
|
continue;
|
|
}
|
|
values.add(node.val);
|
|
if (node.left != null) {
|
|
q.offer(node.left);
|
|
}
|
|
if (node.right != null) {
|
|
q.offer(node.right);
|
|
}
|
|
}
|
|
|
|
return results;
|
|
}
|
|
}
|