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 as:
[ [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, 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] ]
/** * 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
原文：http://www.cnblogs.com/lilyfindjobs/p/4068330.html