Binary Search in Array not working

Question

I am working on a program that will get user input and then store it in an array. Then, it will search the array to see if the number entered by the user is a duplicate or not. For some reason binarySearch is not detecting duplication.

My code is:

import java.util.Arrays;
import java.util.Scanner;

public class Duplicate_Elimination 
{
   public static void main(String[] args) 
   {

   int [] numbers = new int[5]; // create an array
   Scanner input = new Scanner(System.in); // create a Scanner

       // Ask user for 5 numbers
       for (int i = 0; i < 5; i++)
       {
           // ask user to type the number
           System.out.printf("Please type number %d:",i+1);
           int number = input.nextInt(); // get user input and store it in number variable

           // check if the number entered is already stored
           int location = Arrays.binarySearch(numbers,number);

           // store the value inside number variable in numbers array 
           numbers[i] = number;

           showArray(numbers);

           // if there is any similarity between numbers, print error message
           if (location >= 0)
               System.out.printf("%s%n","error");
       } // end for
   }

   // this method will show what's in the array
   public static void showArray(int[] numbers)
   {
       System.out.printf("%n%n"); // print black spaces

       // print all the numbers stored in the array
       for(int digit: numbers)
       {
           System.out.printf("%d",digit);
       }

       System.out.printf("%n"); // print black space
   }
}

I tried my very best to solve but when ever I type 1 as all my numbers, it only show duplication after typing like 3 numbers. It should detect duplication after each entry. Can you please help me figure out what's wrong with my code. I will really appreciate that.

Thanks!!

binary search requires your array is sorted- doesn't look like that is the case — Sarang
– Sarang, Commented Apr 22, 2015 at 0:16
Not really i can use anything. But i didnt find anything else to use so i used Arrays. — Deep
– Deep, Commented Apr 22, 2015 at 0:22

M. Shaw · Accepted Answer · 2015-04-22 00:19:11Z

3

From the java.util.Arrays documentation:

public static int binarySearch(int[] a, int key)

Searches the specified array of ints for the specified value using the binary search algorithm. The array must be sorted (as by the sort(int[]) method) prior to making this call. If it is not sorted, the results are undefined.

So you need to sort the array after every insertion.

answered Apr 22, 2015 at 0:19

M. Shaw

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1 Comment

Deep Over a year ago

Thanks for your reply. I was not sorting my array. So I will fix that now :)

sqluser · Accepted Answer · 2015-04-22 01:00:45Z

0

From what I can see I think taking out the similarity by commenting it out should work.

showArray(numbers);

       // if there is any similarity between numbers, print error message
       //if (location >= 0)
           //System.out.printf("%s%n","error");
   } // end for
 }

edited Apr 22, 2015 at 1:00

sqluser

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answered Apr 22, 2015 at 0:38

Aaron Ferguson

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