[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 }