《程序员代码面试指南》第三章 二叉树问题 遍历二叉树的神级方法 morris

题目

遍历二叉树的神级方法 morris

java代码

package com.lizhouwei.chapter3;

/**
 * @Description:遍历二叉树的神级方法 morris
 * @Author: lizhouwei
 * @CreateDate: 2018/4/14 17:15
 * @Modify by:
 * @ModifyDate:
 */
public class Chapter3_5 {
    //morris中序
    public void morrisInOrder(Node head) {
        Node cur1 = head;
        Node cur2 = null;//左子节点
        while (cur1 != null) {
            cur2 = cur1.left;//当前节点的左子节点
            if (cur2 != null) {
                //循环遍历到左子节点的最右子节点
                while (cur2.right != null && cur2.right != cur1) {
                    cur2 = cur2.right;
                }
                //如过最右节点未指向cur1，则使之指向cur1,并略过后续代码;
                if (cur2.right == null) {
                    cur2.right = cur1;
                    cur1 = cur1.left;
                    continue;
                } else {
                    //如过最右节点已指向cur1，恢复，则使之指向null,
                    cur2.right = null;
                }
            }
            //如果cur1.left 为null,则说明没有左子树,则开始打印父节点;
            System.out.print(cur1.value + " ");
            cur1 = cur1.right;
        }
        System.out.println();
    }

    //morris前序
    public void morrisPreOrder(Node head) {
        Node cur1 = head;
        Node cur2 = null;//左子节点
        while (cur1 != null) {
            cur2 = cur1.left;//当前节点的左子节点
            if (cur2 != null) {
                //循环遍历到左子节点的最右子节点
                while (cur2.right != null && cur2.right != cur1) {
                    cur2 = cur2.right;
                }
                //如过最右节点未指向cur1，则使之指向cur1,并略过后续代码;
                if (cur2.right == null) {
                    cur2.right = cur1;
                    System.out.print(cur1.value + " ");//遇见父节点，先打印父节点
                    cur1 = cur1.left;
                    continue;
                } else {
                    //如过最右节点已指向cur1，恢复，则使之指向null,
                    cur2.right = null;
                }
            } else {
                //如果cur1.left 为null,说明没有左子节点,在切换到右子树之前先打印父节点
                System.out.print(cur1.value + " ");
            }
            cur1 = cur1.right;
        }
        System.out.println();
    }

    //morris后序
    public void morrisPostOrder(Node head) {
        Node cur1 = head;
        Node cur2 = null;//左子节点
        while (cur1 != null) {
            cur2 = cur1.left;//当前节点的左子节点
            if (cur2 != null) {
                //循环遍历到左子节点的最右子节点
                while (cur2.right != null && cur2.right != cur1) {
                    cur2 = cur2.right;
                }
                //如过最右节点未指向cur1，则使之指向cur1,并略过后续代码;
                if (cur2.right == null) {
                    cur2.right = cur1;
                    cur1 = cur1.left;
                    continue;
                } else {
                    //如过最右节点已指向cur1，恢复，则使之指向null,
                    cur2.right = null;
                    printEdge(cur1.left);
                }
            }
            cur1 = cur1.right;
        }
        printEdge(head);
        System.out.println();
    }

    //打印节点
    public void printEdge(Node head) {
        Node tail = reverse(head);
        Node cur = tail;
        while (cur != null) {
            System.out.print(cur.value + " ");
            cur = cur.right;
        }
        //恢复链表
        reverse(tail);
    }

    //反转节点的右子节点链
    public Node reverse(Node head) {
        Node pre = null;
        Node next = null;
        while (head != null) {
            next = head.right;
            head.right = pre;
            pre = head;
            head = next;
        }
        return pre;
    }

    //测试
    public static void main(String[] args) {
        Chapter3_5 chapter = new Chapter3_5();
        int[] arr = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
        Node head = NodeUtil.generTree(arr, 0, arr.length - 1);
        System.out.print("morris中序遍历：");
        chapter.morrisInOrder(head);
        System.out.print("非递归中序遍历：");
        NodeUtil.inOrder(head);
        System.out.println();
        System.out.print("morris前序遍历：");
        chapter.morrisPreOrder(head);
        System.out.print("非递归前序遍历：");
        NodeUtil.preOrder(head);
        System.out.print("morris后序遍历：");
        chapter.morrisPostOrder(head);
        System.out.print("非递归后序遍历：");
        NodeUtil.postOrder(head);
    }
}