树的层次遍历【队列的应用】

思想：将不空的根节点入队列，队列不空的时候出队列，访问该节点，然后分别将左右孩子入队列，正好先出左，再出右，跟队列契合。

java实现代码;

package com.mytest.mymain;
import java.util.LinkedList;
import java.util.Queue;
import java.util.Stack;
class BTree{
    public int value;  //public static int value;  那么最终输出都为8个8
    public BTree left;  
    public BTree right;  
    BTree(int x) { value = x; }  
}
public class TraversalTree {
    public static void main(String[] args) {
        BTree root=new BTree(1);
        BTree Node2=new BTree(2);
        BTree Node3=new BTree(3);
        BTree Node4=new BTree(4);
        BTree Node5=new BTree(5);
        BTree Node6=new BTree(6);
        BTree Node7=new BTree(7);
        BTree Node8=new BTree(8);
    
        root.left=Node2;
        root.right=Node3;
        
        Node2.left=Node4;
        Node2.right=Node5;
        
        Node3.left=Node6;
        Node3.right=Node7;
        
        Node4.left=Node8;
        
        System.out.println("层次遍历");
        levelorder(root);
    }
    //层次遍历
    public static void levelorder(BTree root){
        Queue<BTree> queue=new LinkedList<BTree>();
        BTree bTree=null;
        
        if(root != null){
            queue.add(root);
        }
        
        while(!queue.isEmpty()){
            bTree=queue.poll();
            System.out.print(bTree.value+"  ");
            if(bTree.left != null){
                queue.add(bTree.left);
            }
            if(bTree.right !=null ){
                queue.add(bTree.right);
                
            }
        }
        
    }
}