《程序员代码面试指南》第三章 二叉树问题 分别用递归和非递归实现二叉树前序、中序、后序遍历

分别用递归和非递归实现二叉树前序、中序、后序遍历

java代码

package com.lizhouwei.chapter3;

import java.util.Stack;

/**
 * @Description:分别用递归和非递归实现二叉树前序、中序、后序遍历
 * @Author: lizhouwei
 * @CreateDate: 2018/4/14 9:32
 * @Modify by:
 * @ModifyDate:
 */
public class Chapter3_1 {
    //前序递归
    public void recPreOrder(Node head) {
        if (head == null) {
            return;
        }
        System.out.print(head.value + " ");
        recPreOrder(head.left);
        recPreOrder(head.right);
    }

    //中序递归
    public void recInOrder(Node head) {
        if (head == null) {
            return;
        }
        recInOrder(head.left);
        System.out.print(head.value + " ");
        recInOrder(head.right);
    }

    //后序递归
    public void recPostOrder(Node head) {
        if (head == null) {
            return;
        }
        recPostOrder(head.left);
        recPostOrder(head.right);
        System.out.print(head.value + " ");
    }

    //------------非递归----------------//
    //前序
    public void preOrder(Node head) {
        if (head == null) {
            return;
        }
        Stack<Node> stack = new Stack<Node>();
        stack.push(head);
        while (!stack.isEmpty()) {
            head = stack.pop();
            System.out.print(head.value + " ");
            if (head.right != null) {
                stack.push(head.right);
            }
            if (head.left != null) {
                stack.push(head.left);
            }
        }
    }

    //中序
    public void inOrder(Node head) {
        if (head == null) {
            return;
        }
        Stack<Node> stack = new Stack<Node>();
        while (!stack.isEmpty() || head != null) {
            if (head != null) {
                stack.push(head);
                head = head.left;
            } else {
                head = stack.pop();
                System.out.print(head.value + " ");
                head = head.right;
            }
        }
    }

    //后序
    public void postOrder(Node head) {
        if (head == null) {
            return;
        }
        Node cur = null;
        Stack<Node> stack = new Stack<Node>();
        stack.push(head);
        while (!stack.isEmpty()) {
            cur = stack.peek();
            if (cur.left != null && cur.left != head && cur.right != head) {
                stack.push(cur.left);
            } else if (cur.right != null && cur.right != head) {
                stack.push(cur.right);
            } else {
                head = stack.pop();
                System.out.print(head.value + " ");
            }
        }
    }

    //测试
    public static void main(String[] args) {
        Chapter3_1 chapter = new Chapter3_1();
        int[] arr = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
        Node head = NodeUtil.generTree(arr, 0, arr.length - 1);
        //前序递归打印
        System.out.print("前序递归打印:");
        chapter.recPreOrder(head);
        System.out.println();
        //前序非递归打印
        System.out.print("前序非递归打印:");
        chapter.preOrder(head);
        System.out.println();
        System.out.println();

        //中序递归打印
        System.out.print("中序递归打印:");
        chapter.recInOrder(head);
        System.out.println();
        System.out.print("中序非递归打印:");
        chapter.inOrder(head);
        System.out.println();
        System.out.println();
        //后序递归打印
        System.out.print("后序递归打印:");
        chapter.recPostOrder(head);
        System.out.println();
        System.out.print("后序非递归打印:");
        chapter.postOrder(head);
    }
}