Java Challenge - Prime Number Finder

discourse-admin · November 10, 2021, 10:33pm

This community-built FAQ covers the “Prime Number Finder” code challenge in Java. You can find that challenge here, or pick any challenge you like from our list.

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wassimchakib99285037 · November 15, 2021, 10:30pm

import java.util.*;

public class PrimeFinder {
  public static void main(String[] args) {
    System.out.println(primeFinder(13));
  }

  public static ArrayList primeFinder(int n) {
    ArrayList<Integer> primeNumbers = new ArrayList<Integer>();
    if(n<2) {
      return primeNumbers;
    }
    for (int i=2; i<=n; i++){
      for(int j=2; j<=i; j++){
        if(i%j==0 && i!=j){
          break;
        }else if(i==j){
          primeNumbers.add(j);
        }
      }
    }

    return primeNumbers;
  }
}

cloud1416694462 · November 15, 2021, 11:53pm

import java.util.*;

public class PrimeFinder {
  public static void main(String[] args) {
    System.out.println(primeFinder(13));
  }

  public static ArrayList primeFinder(int n) {
    // Write your code here
    ArrayList<Integer> arr = new ArrayList<>();

    if(n == 1)
    {
      return arr;
    }

    for(int i = 1; i <= n; i++)
    {
      int counter = 0;
      for(int j = 2; j <= i/2; j++)
      {
        if(i % j == 0)
        {
          counter++;
        }
      }

      if(counter == 0 && i != 1)
      {
        arr.add(i);
      }
    }

    return arr;
  }
}

tagwhiz90829 · November 16, 2021, 1:45am

import java.util.*;

public class PrimeFinder {
  public static void main(String[] args) {
    System.out.println(primeFinder(13));
  }

  public static ArrayList primeFinder(int n) {
 ArrayList<Integer> integerArray = new ArrayList<Integer>();
        
        for (int i = 1; i <= n; i++) {
            int count = 0;
            for (int j = i; j >= 1; j--) {
                if (i % j == 0) {
                    count++;
                }
            }
            if (count == 2) {
                integerArray.add(i);
            }
              
        }
        return integerArray;
  }
}

kutote · November 16, 2021, 6:39am

import java.util.ArrayList;

public class PrimeFinder {
    public static void main(String[] args) {
        System.out.println(primeFinder(13));
    }

    public static ArrayList primeFinder(int n) {
       ArrayList <Integer> out = new ArrayList<>();
       for (int i = 2; i <= n; i++){
           boolean isPrime = true;
           for (int j = 2; j < i; j++){
               if (i % j == 0) {
                   isPrime = false;
                   break;
               }
           }
           if (isPrime) out.add(i);
       }
       return out;
    }
}

abcddcba114114 · November 16, 2021, 2:04pm

import java.util.*;

public class PrimeFinder {
  public static void main(String[] args) {
    System.out.println(primeFinder(13));
  }

  public static ArrayList primeFinder(int n) {
    // Write your code here
    ArrayList result = new ArrayList();
    for(int i=2;i<=n;i++){
      if(isPrime(i)){
        result.add(i);
      }
    }
    return result;
  }

  public static boolean isPrime(int n) {
    int count = 0;
    boolean result;
    for(int i=1;i<=n;i++){
      if(n%i==0){
        count++;
      }
    }
    System.out.printf("%d%d\n", count, n);
    result = count == 2?true:false;
    return result;
  }
}

rabiebelkaida · November 16, 2021, 6:50pm

alanlo2378367618 · April 20, 2022, 8:10am

import java.util.*;

public class PrimeFinder {
  public static void main(String[] args) {
    System.out.println(primeFinder(13));
  }

  public static ArrayList primeFinder(int n) {
    // Write your code here
    ArrayList<Integer> primeList = new ArrayList<Integer>();
    for (int i=2;i<=n; i++) {
      if (i==2) {
        primeList.add(i);
      } else {
        boolean divisible = false;
        for (int j : primeList) {
          if (i % j == 0) {
            divisible = true;
            break;
          }
        }
        if (!divisible) {
          primeList.add(i);
        }
      }
    }
    return primeList;
  }
}

ctrlvaultdel · June 29, 2022, 7:39pm

import java.util.*;

public class PrimeFinder {
  public static void main(String[] args) {
    System.out.println(primeFinder(13));
  }

  public static ArrayList primeFinder(int n) {
    ArrayList<Integer> intArrayList = new ArrayList<Integer>();
    if(n < 2){
      return intArrayList;
    }
    for(int i = 2; i <= n; i++){
      boolean isPrime = true;
      for(int j = 2; j < n/2; j++){
        if(i == j) continue;
        if(i % j == 0){
          isPrime = false;
          break;
        }
      }
      if(isPrime){
        intArrayList.add(i);
      }
    }
    return intArrayList;
  }
}

alxbx · July 6, 2022, 10:53am

import java.util.*;

public class PrimeFinder {
  public static void main(String[] args) {
    System.out.println(primeFinder(13));
  }

  public static ArrayList primeFinder(int n) {
    // Write your code here
   
   ArrayList<Integer> primeNo = new ArrayList<Integer>();
   
   for(int i=2; i <= n; i++){
     if((i%2!=0 && i%3!=0 && i%5!=0 && i%7!=0) || i == 2 || i == 3 || i == 5 || i == 7){
        primeNo.add(i);
      }
    }
    return primeNo;
  }
}

janbazant1107978602 · August 22, 2022, 8:39pm

I tried the Sieve of Erastothenes algorithm for this challenge.

  public static boolean[] SieveOfErastothenes(int limit) {
    if (limit < 0) {
      return new boolean[0];
    }
    else if (limit == 0) {
      return new boolean[]{false};
    }
    else if (limit == 1) {
      return new boolean[]{false, false};
    }
    boolean[] isPrimes = new boolean[limit + 1];
    Arrays.fill(isPrimes, true); // set all values to true
    isPrimes[0] = false;
    isPrimes[1] = false;
    double maxFactor = Math.sqrt(limit);
    for (int i = 2; i <= maxFactor; i++) {
      if (isPrimes[i]) {
        for (int j = i * i; j <= limit; j += i) {
          isPrimes[j] = false;
        }
      }
    }
    return isPrimes;
  }

  public static ArrayList<Integer> primeFinder(int n) {
    ArrayList<Integer> primes = new ArrayList<Integer>();
    boolean[] sieve = SieveOfErastothenes(n);
    for (int i = 2; i <= n; i++) {
      if (sieve[i]) {
        primes.add(i);
      }
    }
    return primes;
  }

cloudninja95171 · September 19, 2022, 10:02pm

import java.util.*;

public class PrimeFinder {
public static void main(String args) {
System.out.println(primeFinder(13));
}

public static ArrayList primeFinder(int n) {
// Write your code here
int flag=0;
ArrayList res = new ArrayList<>();
for(int i = 2;i<=n;i++){
for(int j=2;j<=i/2;j++){
if(i%j==0){
flag=1;
break;
}
}
if(flag==0)
res.add(i);
flag=0;
}
return res;
}
}

flyingcarbonaramonst · December 10, 2022, 4:22pm

import java.util.*;

public class PrimeFinder {
  public static void main(String[] args) {
    System.out.println(primeFinder(13));
  }

  public static ArrayList primeFinder(int n) {
    // Write your code here
    ArrayList<Integer> primes = new ArrayList<>();

    if (n < 2) {
      return primes;
    }
    for (int i = 2; i <= n; i++) {
      if (isPrime(i)) {
        primes.add(i);
      }
    }
    return primes;
  }
  public static boolean isPrime(int number) {
    for (int i = 2; i < number; i++){
      if (number % i == 0) {
        return false;
      } 
    }
    return true;
  }
}