Leetcode binary tree level order traversal I II

Given a binary tree, return the level order traversal of its nodes‘ values. (ie, from left to right, level by level).

For example:
Given Binary Tree{3,9,20,#,#,15,7},

    3   /   9  20    /     15   7

Return its level order traversal:

[  [3],  [9,20],  [15,7]]

/** * Definition for binary tree * public class TreeNode { *     int val; *     TreeNode left; *     TreeNode right; *     TreeNode(int x) { val = x; } * } */public class Solution {    public ArrayList<ArrayList<Integer>> levelOrder(TreeNode root) {        ArrayList<ArrayList<Integer>> result=new  ArrayList<ArrayList<Integer>>();        if(root==null){            return result;        }        LinkedList<TreeNode> queue = new LinkedList<TreeNode>();        queue.add(root);        while(!queue.isEmpty()){            ArrayList<Integer> level=new ArrayList<Integer>();            int size=queue.size();            for(int i=0;i<size;i++){                TreeNode head=queue.poll();                level.add(head.val);                if(head.left!=null){                    queue.add(head.left);                }                if(head.right!=null){                    queue.add(head.right);                }            }            result.add(level);        }        return result;    }}

Binary Tree level order traversal II

Given a binary tree, returnBottom-up level orderTraversal 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:

[  [15,7],  [9,20],  [3]]

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

 

Leetcode binary tree level order traversal I II