标签：collect height res bin values bottom == else nod
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] ]
/** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode(int x) { val = x; } * } */ class Solution { public List<List<Integer>> levelOrderBottom(TreeNode root) { List<List<Integer>> res = new ArrayList<List<Integer>>(); levelHelper(res, root, 0); Collections.reverse(res); return res; } public void levelHelper(List<List<Integer>> res, TreeNode root, int height) { if (root == null) return; if (height == res.size()) { res.add(new ArrayList<Integer>()); } res.get(height).add(root.val); levelHelper(res, root.left, height+1); levelHelper(res, root.right, height+1); } }
Collections.reverse(ArrarList) return void instead of arraylist or anything else.
107. Binary Tree Level Order Traversal II
标签：collect height res bin values bottom == else nod
原文地址：https://www.cnblogs.com/wentiliangkaihua/p/10493585.html
