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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,#,#,15,7},
3 / \ 9 20 / \ 15 7
return its bottom-up level order traversal as:
[ [15,7], [9,20], [3]]
confused what "{1,#,2,3}" means?
/** * Definition for binary tree * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode(int x) { val = x; } * } */public class Solution { public static ArrayList > levelOrderBottom(TreeNode root) { // Note: The Solution object is instantiated only once and is reused by each test case. LinkedList > answer = new LinkedList >(); if (root != null) { LinkedList currentLevelNode = new LinkedList (); currentLevelNode.add(root); while (!currentLevelNode.isEmpty()) { ArrayList temp = new ArrayList (currentLevelNode.size()); LinkedList nextLevelNode = new LinkedList (); for (TreeNode node : currentLevelNode) { temp.add(node.val); if (node.left != null) { nextLevelNode.add(node.left); } if (node.right != null) { nextLevelNode.add(node.right); } } answer.add(0, temp); currentLevelNode = nextLevelNode; } } return new ArrayList >(answer); }} 转载地址：http://nnuni.baihongyu.com/