二叉树的广度优先遍历

package com.dengpf.BinaryTreeLevelOrderTraversal;

import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
import java.util.Queue;

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 * int val;
 * TreeNode left;
 * TreeNode right;
 * TreeNode(int x) { val = x; }
 * }
 */
public class Solution {

    List<List<Integer>> rlist = new ArrayList<List<Integer>>();
    private Queue<TreeNode> queue = new LinkedList<TreeNode>();

    public List<List<Integer>> levelOrder(TreeNode root) {
        if (root == null) {
            return rlist;
        }

        queue.offer(root);


        while (true) {
            int length = queue.size();
            if (length == 0) {
                break;
            }
            List<Integer> innerList = new ArrayList<Integer>();
            while (length > 0) {
                TreeNode headNode = queue.poll();

                innerList.add(headNode.val);

                if (headNode.left != null) {
                    queue.offer(headNode.left);
                }
                if (headNode.right != null) {
                    queue.offer(headNode.right);

                }
                length--;
            }
            rlist.add(innerList);

        }

        return rlist;
    }
}