Java实现二叉树的深度优先遍历和广度优先遍历算法示例

package BinaryTreeTraverseTest;
import java.util.LinkedList;
import java.util.Queue;
/**
 * 二叉树的深度优先遍历和广度优先遍历
 * @author Fantasy
 * @version 1.0 2016/10/05 - 2016/10/07
 */
public class BinaryTreeTraverseTest {
  public static void main(String[] args) {
  BinarySortTree<Integer> tree = new BinarySortTree<Integer>();
    tree.insertNode(35);
    tree.insertNode(20);
    tree.insertNode(15);
    tree.insertNode(16);
    tree.insertNode(29);
    tree.insertNode(28);
    tree.insertNode(30);
    tree.insertNode(40);
    tree.insertNode(50);
    tree.insertNode(45);
    tree.insertNode(55);
    System.out.print("先序遍历（递归）：");
    tree.preOrderTraverse(tree.getRoot());
    System.out.println();
    System.out.print("中序遍历（递归）：");
    tree.inOrderTraverse(tree.getRoot());
    System.out.println();
    System.out.print("后序遍历（递归）：");
    tree.postOrderTraverse(tree.getRoot());
    System.out.println();
    System.out.print("先序遍历（非递归）：");
    tree.preOrderTraverseNoRecursion(tree.getRoot());
    System.out.println();
    System.out.print("中序遍历（非递归）：");
    tree.inOrderTraverseNoRecursion(tree.getRoot());
    System.out.println();
    System.out.print("后序遍历（非递归）：");
    tree.postOrderTraverseNoRecursion(tree.getRoot());
    System.out.println();
    System.out.print("广度优先遍历：");
    tree.breadthFirstTraverse(tree.getRoot());
  }
}
/**
 * 结点
 */
class Node<E extends Comparable<E>> {
  E value;
  Node<E> left;
  Node<E> right;
  Node(E value) {
    this.value = value;
    left = null;
    right = null;
  }
}
/**
 * 使用一个先序序列构建一棵二叉排序树（又称二叉查找树）
 */
class BinarySortTree<E extends Comparable<E>> {
  private Node<E> root;
  BinarySortTree() {
    root = null;
  }
  public void insertNode(E value) {
    if (root == null) {
      root = new Node<E>(value);
      return;
    }
    Node<E> currentNode = root;
    while (true) {
      if (value.compareTo(currentNode.value) > 0) {
        if (currentNode.right == null) {
          currentNode.right = new Node<E>(value);
          break;
        }
        currentNode = currentNode.right;
      } else {
        if (currentNode.left == null) {
          currentNode.left = new Node<E>(value);
          break;
        }
        currentNode = currentNode.left;
      }
    }
  }
  public Node<E> getRoot(){
    return root;
  }
  /**
   * 先序遍历二叉树（递归）
   * @param node
   */
  public void preOrderTraverse(Node<E> node) {
    System.out.print(node.value + " ");
    if (node.left != null)
      preOrderTraverse(node.left);
    if (node.right != null)
      preOrderTraverse(node.right);
  }
  /**
   * 中序遍历二叉树（递归）
   * @param node
   */
  public void inOrderTraverse(Node<E> node) {
    if (node.left != null)
      inOrderTraverse(node.left);
    System.out.print(node.value + " ");
    if (node.right != null)
      inOrderTraverse(node.right);
  }
  /**
   * 后序遍历二叉树（递归）
   * @param node
   */
  public void postOrderTraverse(Node<E> node) {
    if (node.left != null)
      postOrderTraverse(node.left);
    if (node.right != null)
      postOrderTraverse(node.right);
    System.out.print(node.value + " ");
  }
  /**
   * 先序遍历二叉树（非递归）
   * @param root
   */
  public void preOrderTraverseNoRecursion(Node<E> root) {
    LinkedList<Node<E>> stack = new LinkedList<Node<E>>();
    Node<E> currentNode = null;
    stack.push(root);
    while (!stack.isEmpty()) {
      currentNode = stack.pop();
      System.out.print(currentNode.value + " ");
      if (currentNode.right != null)
        stack.push(currentNode.right);
      if (currentNode.left != null)
        stack.push(currentNode.left);
    }
  }
  /**
   * 中序遍历二叉树（非递归）
   * @param root
   */
  public void inOrderTraverseNoRecursion(Node<E> root) {
    LinkedList<Node<E>> stack = new LinkedList<Node<E>>();
    Node<E> currentNode = root;
    while (currentNode != null || !stack.isEmpty()) {
      // 一直循环到二叉排序树最左端的叶子结点（currentNode是null）
      while (currentNode != null) {
        stack.push(currentNode);
        currentNode = currentNode.left;
      }
      currentNode = stack.pop();
      System.out.print(currentNode.value + " ");
      currentNode = currentNode.right;
    }
  }
  /**
   * 后序遍历二叉树（非递归）
   * @param root
   */
  public void postOrderTraverseNoRecursion(Node<E> root) {
    LinkedList<Node<E>> stack = new LinkedList<Node<E>>();
    Node<E> currentNode = root;
    Node<E> rightNode = null;
    while (currentNode != null || !stack.isEmpty()) {
      // 一直循环到二叉排序树最左端的叶子结点（currentNode是null）
      while (currentNode != null) {
        stack.push(currentNode);
        currentNode = currentNode.left;
      }
      currentNode = stack.pop();
      // 当前结点没有右结点或上一个结点（已经输出的结点）是当前结点的右结点，则输出当前结点
      while (currentNode.right == null || currentNode.right == rightNode) {
        System.out.print(currentNode.value + " ");
        rightNode = currentNode;
        if (stack.isEmpty()) {
          return; //root以输出，则遍历结束
        }
        currentNode = stack.pop();
      }
      stack.push(currentNode); //还有右结点没有遍历
      currentNode = currentNode.right;
    }
  }
  /**
   * 广度优先遍历二叉树，又称层次遍历二叉树
   * @param node
   */
  public void breadthFirstTraverse(Node<E> root) {
    Queue<Node<E>> queue = new LinkedList<Node<E>>();
    Node<E> currentNode = null;
    queue.offer(root);
    while (!queue.isEmpty()) {
      currentNode = queue.poll();
      System.out.print(currentNode.value + " ");
      if (currentNode.left != null)
        queue.offer(currentNode.left);
      if (currentNode.right != null)
        queue.offer(currentNode.right);
    }
  }
}