课堂随笔

package project;

import java.util.ArrayList;
import java.util.Scanner;


public class read1
{
    class KadaneResult
    {
        int maxSum;
        int start;
        int end;

        public KadaneResult(int maxSum, int start, int end)
        {
            this.maxSum = maxSum;
            this.start = start;
            this.end = end;
        }
    }

    public ArrayList<String> kadane(int arr[])
    {
        ArrayList<String> process = new ArrayList<>();
        int max = 0;
        int maxStart = -1;
        int maxEnd = -1;
        int currentStart = 0;
        int maxSoFar = 0;
        for (int i = 0; i < arr.length; i++)
        {
            maxSoFar += arr[i];
            if (maxSoFar < 0)
            {
                maxSoFar = 0;
                currentStart = i + 1;
            }
            if (max < maxSoFar)
            {
                maxStart = currentStart;
                maxEnd = i;
                max = maxSoFar;
            }
            process.add(i + ":" + printOut(arr, maxStart, maxEnd, maxSoFar));
        }
        return process;
    }

    private String printOut(int arr[], int maxStart, int maxEnd, int maxSoFar)
    {
        String aString = new String();
        for (int i = 0; i < arr.length; i++)
        {

            if (i == maxStart || i == maxEnd)
            {
                aString += ("[" + arr[i] + "]");
            } else
            {
                aString += (arr[i]);
            }
            if (i < arr.length - 1)
            {
                aString += (" ");
            } else
            {
                aString += (" \n当前最大子数组和为{" + maxSoFar + "}");
            }
        }
        return aString;
    }

    public static void main(String[] args)
    {
        read1 arrayList = new read1();
        int[] a = { 1, 3, -9, 6, 2, 4, 1, 5, 8 };
        ArrayList<String> arrayList2 = arrayList.kadane(a);
        Scanner inScanner = new Scanner(System.in);
        int i = -1;
        boolean flag = true;
        while (flag)
        {
            System.out.println("1.下一步 2.上一步 3.回滚到第几步");
            switch (inScanner.nextInt())
            {
            case -1:
                System.out.println("已经到顶");
            case 1:
                if (i + 1 >= arrayList2.size())
                {
                    System.out.println("已经到底");
                    break;
                }
                System.out.println(arrayList2.get(++i));
                break;
            case 2:
                System.out.println(arrayList2.get(--i));
                break;
            case 3:
                System.out.println("回滚到第..步");
                i = inScanner.nextInt();
                System.out.println(arrayList2.get(i));
                break;
            default:
                flag = false;
                break;
            }

        }
    }
}