《程序员代码面试指南》第三章 二叉树问题 先序、中序和后序数组两两结合重构二叉树

先序、中序和后序数组两两结合重构二叉树

先序、中序和后序数组两两结合重构二叉树

java代码

package com.lizhouwei.chapter3;

import java.util.HashMap;
import java.util.Map;

/**
 * @Description:先序、中序和后序数组两两结合重构二叉树
 * @Author: lizhouwei
 * @CreateDate: 2018/4/16 19:53
 * @Modify by:
 * @ModifyDate:
 */
public class Chapter3_21 {

    //前序和中序数组组成二叉树
    public Node preInToTree(int[] pre, int[] in) {
        if (pre == null || in == null) {
            return null;
        }
        Map<Integer, Integer> map = new HashMap<>();
        for (int i = 0; i < in.length; i++) {
            map.put(in[i], i);
        }
        return preAndIn(pre, 0, pre.length - 1, in, 0, in.length - 1, map);
    }

    public Node preAndIn(int[] pre, int preStart, int preEnd, int[] in, int inStart, int inEnd, Map<Integer, Integer> map) {
        if (preStart > preEnd) {
            return null;
        }
        int value = pre[preStart];
        Node head = new Node(value);
        int index = map.get(value);

        head.left = preAndIn(pre, preStart + 1, preStart + index - inStart, in, inStart, index - 1, map);
        head.right = preAndIn(pre, preStart + index - inStart + 1, preEnd, in, index + 1, inEnd, map);

        return head;
    }

    //中序和后序数组组成二叉树
    public Node inPosToTree(int[] in, int[] pos) {
        if (in == null || pos == null) {
            return null;
        }
        Map<Integer, Integer> map = new HashMap<>();
        for (int i = 0; i < in.length; i++) {
            map.put(in[i], i);
        }
        return inAndPos(in, 0, in.length - 1, pos, 0, pos.length - 1, map);
    }

    public Node inAndPos(int[] in, int inStart, int inEnd, int[] pos, int posStart, int posEnd, Map<Integer, Integer> map) {
        if (posStart > posEnd) {
            return null;
        }
        int value = pos[posEnd--];
        Node head = new Node(value);
        int index = map.get(value);

        head.left = inAndPos(in, inStart, index - 1, pos, posStart, posStart + index - inStart - 1, map);
        head.right = inAndPos(in, index + 1, inEnd, pos, posStart + index - inStart, posEnd, map);

        return head;
    }

    //前序和后序数组组成二叉树
    public Node prePosToTree(int[] pre, int[] pos) {
        if (pre == null || pos == null) {
            return null;
        }
        Map<Integer, Integer> map = new HashMap<>();
        for (int i = 0; i < pos.length; i++) {
            map.put(pos[i], i);
        }
        return preAndPos(pre, 0, pre.length - 1, pos, 0, pos.length - 1, map);
    }

    public Node preAndPos(int[] pre, int preStart, int preEnd, int[] pos, int posStart, int posEnd, Map<Integer, Integer> map) {
        if (preStart > preEnd) {
            return null;
        }
        int value = pos[posEnd--];
        Node head = new Node(value);
        if (preStart == preEnd) {
            return head;
        }
        int index = map.get(pre[++preStart]);

        head.left = preAndPos(pre, preStart, preStart + index - posStart, pos, posStart, index, map);
        head.right = preAndPos(pre, preStart + index - posStart + 1, preEnd, pos, index + 1, posEnd, map);

        return head;
    }

    //测试
    public static void main(String[] args) {
        Chapter3_21 chapter = new Chapter3_21();
        int[] pre = {5, 2, 1, 3, 4, 8, 6, 7, 9, 10};
        int[] in = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
        int[] pos = {1, 4, 3, 2, 7, 6, 10, 9, 8, 5};

        Node head = chapter.preInToTree(pre, in);
        System.out.println("前序数组：pre = {5, 2, 1, 3, 4, 8, 6, 7, 9, 10}");
        System.out.println("中序数组：in = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10}");
        System.out.println("后序数组：pos = {1, 4, 3, 2, 7, 6, 10, 9, 8, 5}");
        System.out.println();
        System.out.println("前序数组和中序数组组成的二叉树:");
        System.out.print("二叉树前序遍历：");
        NodeUtil.preOrder(head);
        System.out.print("二叉树中序遍历：");
        NodeUtil.inOrder(head);
        System.out.println();
        head = chapter.inPosToTree(in, pos);
        System.out.println("后序数组和中序数组组成的二叉树:");
        System.out.print("二叉树后序遍历：");
        NodeUtil.postOrder(head);
        System.out.print("二叉树中序遍历：");
        NodeUtil.inOrder(head);
        System.out.println();
        head = chapter.prePosToTree(pre, pos);
        System.out.println("前序数组和后序数组组成的二叉树:");
        System.out.print("二叉树前序遍历：");
        NodeUtil.preOrder(head);
        System.out.print("二叉树后序遍历：");
        NodeUtil.postOrder(head);
    }
}