二分查找找到不重复java的元素

Question

//package alg;
import java.io.*;

//import java.io.File;
//import java.io.FileNotFoundException;
//import java.io.InvalidCommandException;
//import java.io.NumberFormatException;
import java.util.Arrays;
//import java.util.ArrayList;
//import java.util.List;
import java.util.Scanner;

//import javax.sound.sampled.Line;

public class FindOut
{
    public static void Find(int [] Ray, int min , int max)
    {


        if(min > max)
        {
            return;
        }

        if(min == max)
        {
            System.out.println(Ray[min]);
            return;

        }

        int med = (min + max)/2;


        if(med % 2 == 0)
        {

            if(Ray[med] == Ray[med + 1])
                Find(Ray, med + 2, max);

            else
                Find(Ray, min, med);

        }

        else //if(med % 2 == 1)
        //{

            if(Ray[med] == Ray[med-1])

                Find(Ray, med + 1 , max);

            else
                Find(Ray, min, med - 1);
    //  }



    }





    public static void main(String [] args) throws FileNotFoundException
    {

        @SuppressWarnings("resource")


        File file = new File(args [0]);

        Scanner scanner = new Scanner(file);


                try
        {

            int[] Ray = new int [5];    

            while(scanner.hasNext())
            {

                String num = scanner.next();



                 Ray = Arrays.stream(num.split(",")).mapToInt(Integer::parseInt).toArray();


                Find(Ray,0, Ray.length-1);





            }


                //  File inputFile = new File(num);


        }
        catch(NumberFormatException ex)
        {

        }

 }
}

What I need is to input a file through command line and it will read the integers inside place them into an array that I send through the function to find the element that appears only once such as

3 , 3 ,48, 48, 65, 95, 95

It should output

65

But what it does is

3 3 48 48 65 95 95

I know its not the function I tested that with hard code and ran through the main logically step by step so can anyone explain the problem?

Answer 1

There is something wrong with how the file is read. It seems the code expects one line to contain the entire list of numbers. However, Scanner uses whitespace as the default delimiter. Find ends up being called once for every number in the file.

To fix it, a delimiter can be specified like so:

Scanner scanner = new Scanner(file).useDelimiter(",");

This means there is no need for the mapToInt thing you were doing. Instead, I recommend you use a container from Collections such as ArrayList , and appending the number to it after conversion to an integer.

public static void main(String[] args) throws FileNotFoundException {
    @SuppressWarnings("resource")
    File file = new File(args [0]);
    Scanner scanner = new Scanner(file).useDelimiter(",");

    try {
        ArrayList<Integer> Ray = new ArrayList<>();

        while (scanner.hasNext()) {
            String num = scanner.next().trim();
            Ray.add(Integer.parseInt(num));
        }

        scanner.close();
        int[] arr = Ray.stream().mapToInt(i -> i).toArray();
        Find(arr, 0, arr.length - 1);
    } catch (NumberFormatException ex) {

    }
}

Using an ArrayList allows it expand as needed, unlike an array, which has a fixed size. This is convenient because it means you don't have to know the amount of integers in the file ahead of time.

To keep compatibility with your Find function, I converted the ArrayList back to a normal array. However, I recommend you update your function to accept an ArrayList .