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


/**
 * 定义二叉树节点元素
 * @author bubble
 *
 */
class Node {  
  public Node leftchild;
  public Node rightchild;
  public int data;

  public Node(int data) {
    this.data = data;
  }

}

public class TestBinTree {
  
  /**
   * 将一个arry数组构建成一个完全二叉树
   * @param arr 需要构建的数组
   * @return 二叉树的根节点
   */
  public Node initBinTree(int[] arr) {
    if(arr.length == 1) {
      return new Node(arr[0]);
    }
    List<Node> nodeList = new ArrayList<>();
    
    for(int i = 0; i < arr.length; i++) {
      nodeList.add(new Node(arr[i]));
    }
    int temp = 0;
    while(temp <= (arr.length - 2) / 2) { //注意这里，数组的下标是从零开始的
      if(2 * temp + 1 < arr.length) {
        nodeList.get(temp).leftchild = nodeList.get(2 * temp + 1);
      }
      if(2 * temp + 2 < arr.length) {
        nodeList.get(temp).rightchild = nodeList.get(2 * temp + 2);
      }
      temp++;
    }
    return nodeList.get(0);
    }
 
  /**
   * 层序遍历二叉树，，并分层打印
   * @param root 二叉树根节点
   *
   */
   public void trivalBinTree(Node root) {
    Queue<Node> nodeQueue = new ArrayDeque<>(); 
    nodeQueue.add(root);
    Node temp = null;
    int currentLevel = 1;  //记录当前层需要打印的节点的数量
    int nextLevel = 0;//记录下一层需要打印的节点的数量
    while ((temp = nodeQueue.poll()) != null) {
      if (temp.leftchild != null) {
        nodeQueue.add(temp.leftchild);
        nextLevel++;
        
      }
      if (temp.rightchild != null) {
        nodeQueue.add(temp.rightchild);
        nextLevel++;
      }
      System.out.print(temp.data + " ");
      currentLevel--;
      if(currentLevel == 0) {
        System.out.println();
        currentLevel = nextLevel;
        nextLevel = 0;
      }
    }
  }
  

   /**
    * 先序遍历
    * @param root 二叉树根节点
    */
    public void preTrival(Node root) {
      if(root == null) {
        return;
      }
      System.out.print(root.data + " ");
      preTrival(root.leftchild);
      preTrival(root.rightchild);
    }
    /**
     * 中序遍历
     * @param root 二叉树根节点
     */
    public void midTrival(Node root) {
      if(root == null) {
        return;
      }
      midTrival(root.leftchild);
      System.out.print(root.data + " ");
      midTrival(root.rightchild);
    }
    /**
     * 后序遍历
     * @param root 二叉树根节点
     */
    public void afterTrival(Node root) {
      if(root == null) {
        return;
        
      }
      afterTrival(root.leftchild);
      afterTrival(root.rightchild);
      System.out.print(root.data + " ");
    }
    
    
    public static void main(String[] args) {
      TestBinTree btree = new TestBinTree();
      int[] arr = new int[] {1,2,3,4,5,6,7};
      Node root = btree.initBinTree(arr);
      System.out.println("层序遍历(分层打印)：");
      btree.trivalBinTree(root);
      System.out.println("\n先序遍历：");
      btree.preTrival(root);
      System.out.println("\n中序遍历：");
      btree.midTrival(root);
      System.out.println("\n后序遍历：");
      btree.afterTrival(root);
      
    }
    
   }