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[Leetcode] 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]]
Solution:
在I的基础上倒过来就好。
1 /** 2 * Definition for binary tree 3 * public class TreeNode { 4 * int val; 5 * TreeNode left; 6 * TreeNode right; 7 * TreeNode(int x) { val = x; } 8 * } 9 */10 public class Solution {11 public List<List<Integer>> levelOrderBottom(TreeNode root) {12 List<List<Integer>> ret=new ArrayList<List<Integer>>();13 if(root==null)14 return ret;15 List<List<Integer>> alal=new ArrayList<List<Integer>>();16 List<Integer> al=new ArrayList<Integer>();17 Queue<TreeNode> queue=new LinkedList<TreeNode>();18 queue.add(root);19 int curLevel=1;20 int nextLevel=0;21 22 while(!queue.isEmpty()){23 TreeNode cur=queue.remove();24 al.add(cur.val);25 curLevel--;26 27 if(cur.left!=null){28 queue.add(cur.left);29 nextLevel++;30 }31 32 if(cur.right!=null){33 queue.add(cur.right);34 nextLevel++;35 }36 37 if(curLevel==0){38 alal.add(al);39 al=new ArrayList<Integer>();40 curLevel=nextLevel;41 nextLevel=0;42 }43 }44 for(int i=alal.size()-1;i>=0;--i){45 ret.add(alal.get(i));46 }47 48 return ret;49 }50 }
[Leetcode] Binary Tree Level Order Traversal II
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