Compare big integers in array

Question

How to find 3 the biggest BigInteger objects in array? This is my code for now.

package masivi;

import java.math.BigInteger;
import java.util.Scanner;

public class largest3Numbers {

    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        int n = scan.nextInt();
        BigInteger[] numbers = new BigInteger[n];
        BigInteger tempbiggest1 = new BigInteger("0");
        BigInteger biggest1 = new BigInteger("0");
        BigInteger tempbiggest2 = new BigInteger("0");
        BigInteger biggest2 = new BigInteger("0");
        BigInteger tempbiggest3 = new BigInteger("0");
        BigInteger biggest3 = new BigInteger("0");

        for (int i = 0; i < numbers.length; i++) {
            numbers[i] = scan.nextBigInteger();
            if (numbers[i] > tempbiggest1) {

            }
        }
    }
}

Jesper · Accepted Answer · 2015-05-30 08:33:27Z

3

This will not compile:

if (numbers[i] > tempbiggest1) {

You cannot use the > operator on BigInteger objects. Use compareTo instead:

// Check if numbers[i] is larger than tempbiggest1
if (numbers[i].compareTo(tempbiggest1) > 0) {

answered May 30, 2015 at 8:33

Jesper

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Comments

Hauke S · Accepted Answer · 2015-05-30 08:56:38Z

1

Just use Array.sort to sort the array and take the last three elements in the array:

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

        BigInteger[] numbers = new BigInteger[6];
        numbers[0] = new BigInteger("10000000");
        numbers[1] = new BigInteger("200000000");
        numbers[2] = new BigInteger("30000000");
        numbers[3] = new BigInteger("5555555555555");
        numbers[4] = new BigInteger("6666666666");
        numbers[5] = new BigInteger("0");

        Arrays.sort(numbers );

        System.out.println("the three biggest are: " + numbers[5] + ", " + numbers[4] + ", " + numbers[3]);

     }
}

answered May 30, 2015 at 8:56

Hauke S

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Comments

user666 · Accepted Answer · 2015-05-30 08:39:38Z

0

First sort the array . You can use one of internal Arrays.sort utility.
In the sorted array you can fetch the elements like this .. a[len-1] , a[len-2],a[len-3] where len is yourarray.length

When we use Arrays.sort the elements should be naturally comparable and BigInteger is and implements comparable interface. Thre are few other approaches as well like copying into TreeSet etc but will have more space complexcity.

answered May 30, 2015 at 8:39

user666

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2 Comments

Tagir Valeev Over a year ago

That's probably an overkill to sort the whole array just to find the three biggest values. This can be slower for large arrays.

user666 Over a year ago

Searching can never be successfull without sorting ... doing it sequentially will have o(n) complexcity ... however you can use modify merge sort/quick sort algorithm a bit for searching to get logarithmic complexity which is complicated for a starter ..

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