leetcode 107 Binary Tree Level Order Traversal II ----- java

標籤：turn   log   evel   int   tom   size   bsp   binary   pre   

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]]

與之前的題做法一樣，就是插入的時候，每次在第一位插入。

 

/** * Definition for a binary tree node. * public class TreeNode { *     int val; *     TreeNode left; *     TreeNode right; *     TreeNode(int x) { val = x; } * } */public class Solution {    public List<List<Integer>> levelOrderBottom(TreeNode root) {                    List list = new ArrayList<List<Integer>>();        if( root == null)            return list;        Queue<TreeNode> tree = new LinkedList<TreeNode>();        tree.add(root);        while( !tree.isEmpty() ){            List ans = new ArrayList<Integer>();            int size = tree.size();            for( int i = 0;i<size;i++){                TreeNode node = tree.poll();                ans.add(node.val);                if( node.left != null )                    tree.add(node.left);                if( node.right != null)                    tree.add(node.right);            }            if( !ans.isEmpty() )                list.add(0,ans);        }        return list;    }}

 

 

 

 

 

leetcode 107 Binary Tree Level Order Traversal II ----- java