LeetCode 102 - Binary Tree Level Order Traversal - 题解/Solution

*https://leetcode.com/problems/binary-tree-level-order-traversal/*

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/**
* Given a binary tree, return the 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,#,#,15,7},
* 3
* / \
* 9 20
* / \
* 15 7
* return its bottom-up level order traversal as:
* [
* [3],
* [9,20],
* [15,7]
* ]
*
* @author dongyuxi
*
*/
public class Solution {
public List<List<Integer>> levelOrder(TreeNode root) {
List<List<Integer>> levelList = new ArrayList<List<Integer>>();
Queue<TreeNode> queue = new LinkedList<TreeNode>();
if (null != root) {
queue.add(root);
int size = queue.size();
List<Integer> list = new ArrayList<Integer>();
while (!queue.isEmpty()) {
TreeNode element = queue.poll();;
list.add(element.val);
size--;
if (null != element.left) {
queue.add(element.left);
}
if (null != element.right) {
queue.add(element.right);
}
if (0 == size) {
levelList.add(list);
list = new ArrayList<Integer>();
size = queue.size();
}
}
}
return levelList;
}
}

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