Java完全二叉樹的創(chuàng)建與四種遍歷方法分析

import java.util.ArrayDeque;
import java.util.ArrayList;
import java.util.List;
import java.util.Queue;
/**
 * 定義二叉樹節(jié)點(diǎn)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 {
  /**
   * 將一個(gè)arry數(shù)組構(gòu)建成一個(gè)完全二叉樹
   * @param arr 需要構(gòu)建的數(shù)組
   * @return 二叉樹的根節(jié)點(diǎn)
   */
  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) { //注意這里，數(shù)組的下標(biāo)是從零開始的
      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);
    }
  /**
   * 層序遍歷二叉樹
   * @param root 二叉樹根節(jié)點(diǎn)
   * @param nodeQueue ，用到的隊(duì)列數(shù)據(jù)結(jié)構(gòu)
   */
   public void trivalBinTree(Node root, Queue<Node> nodeQueue) {
    nodeQueue.add(root);
    Node temp = null;
    while ((temp = nodeQueue.poll()) != null) {
      System.out.print(temp.data + " ");
      if (temp.leftchild != null) {
        nodeQueue.add(temp.leftchild);
      }
      if (temp.rightchild != null) {
        nodeQueue.add(temp.rightchild);
      }
    }
  }
   /**
    * 先序遍歷
    * @param root 二叉樹根節(jié)點(diǎn)
    */
    public void preTrival(Node root) {
      if(root == null) {
        return;
      }
      System.out.print(root.data + " ");
      preTrival(root.leftchild);
      preTrival(root.rightchild);
    }
    /**
     * 中序遍歷
     * @param root 二叉樹根節(jié)點(diǎn)
     */
    public void midTrival(Node root) {
      if(root == null) {
        return;
      }
      midTrival(root.leftchild);
      System.out.print(root.data + " ");
      midTrival(root.rightchild);
    }
    /**
     * 后序遍歷
     * @param root 二叉樹根節(jié)點(diǎn)
     */
    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);
      Queue<Node> nodeQueue = new ArrayDeque<>();
      System.out.println("億速云測(cè)試結(jié)果：");
      System.out.println("層序遍歷：");
      btree.trivalBinTree(root, nodeQueue);
      System.out.println("\n先序遍歷：");
      btree.preTrival(root);
      System.out.println("\n中序遍歷：");
      btree.midTrival(root);
      System.out.println("\n后序遍歷：");
      btree.afterTrival(root);
    }
}