CODEWITHSUNDEEP
javaarrayswhile-loop
Morgan
Morgan

Reputation: 3

While loop that will cycle through entries in array java

Alright so I'm trying to set up a program that will find prime numbers. I've set up an array called primes with prime numbers up to 199. How can I create a while loop that pretty much says, while (x%primes[any number in primes] <= 0). I'm not sure what I should be putting to make it properly detect it. I know or statements are an option, I'm just wondering if there's a better way. Here's my code:

import static java.lang.System.out;
public class Problem3 {

public static void main(String[] args) {
    /// What is the largest prime factor of the number 600851475143 ?
        long x;
        x = 600851475143L;
        int[] primes = {
            2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 101, 103, 107, 109, 113, 127, 131, 137, 139, 149, 151, 157, 163, 167, 173, 179, 181, 191, 193, 197, 199,
        };
        out.println(x);
        //while (x % primes[*This is where I need clarification*] <= 0) {
            int i = 0;

                for (i = 0; i < primes.length; i++) {
                    //out.println("Term " + i + " is " + primes[i]);
                        if (x%primes[i] <=0) {
                            x = x/primes[i];
                        }

                }   
        //}

        out.println(x);

}

}

This answer worked for me!

Upvotes: 0

Views: 37

Answers (1)

Elliott Frisch
Elliott Frisch

Reputation: 201439

Your table of primes is too small (only 71 is a factor of 600851475143L). Easiest fix, eliminate that table and iterate from three to the square root of your number incrementing by two. Like,

long x = 600851475143L;
for (int i = 3; i <= Math.sqrt(x); i += 2) {
    if (x % i == 0) {
        System.out.println(i);
        x /= i;
    }
}
System.out.println(x);

I get

71
839
1471
6857

And

71*839*1471*6857
600851475143

Upvotes: 1

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