微软算法100题16 按层遍历二叉树

第16 题：
题目（微软）：
输入一颗二元树，从上往下按层打印树的每个结点，同一层中按照从左往右的顺序打印。
例如输入
8
/
6 10
/ /
5 7 9 11
输出8 6 10 5 7 9 11

思路：遇到这种按层执行或者按次序执行的动作，一般会联想到队列

package com.rui.microsoft;

import java.util.ArrayDeque;
import java.util.Deque;

public class Test16_TraverseTreeHorizontal {

    public static void main(String[] args) {
        Node node4 = new Node(4);
        Node node3 = new Node(3);
        Node node5 = new Node(5);
        Node node2 = new Node(2);
        
        node4.left = node3;
        node4.right = node5;
        node3.left = node2;
        
        Test16_TraverseTreeHorizontal.traverse(node4);
    }
    
    public static void traverse(Node node){
        Node head = node;
        
        if(null == head) return;
        //leaf
        if(null == head.left && null == head.right){
            System.out.println(head.value);
            return;
        }
        
        //Non-leaf
        Deque<Node> queue = new ArrayDeque<Node>();
        queue.offer(head);
        
        while(!queue.isEmpty()){
            Node n = queue.poll();
            System.out.println(n.value);
            Node left = n.left;
            Node right = n.right;
            if(null != left)queue.offer(left);
            if(null != right)queue.offer(right);
        }
        
    }
    
    static class Node{
        int value;
        Node left;
        Node right;
        Node(int v){
            this.value = v;
        }
    }
}