CODEWITHSUNDEEP
javanumbersfactorization
Moe
Moe

Reputation: 19

Finding the smallest integer that is a factor of C?

I need help with this method smallestFactor

public static int smallestFactor(int C) This function takes as its argument an integer C, and it returns the smallest integer that is a factor of C, other than 1.

Parameters: C - An integer to factor.

Precondition: C must be greater than 1.

Returns: The smallest factor of C.

public class Factor
{       
public static long smallestFactor(int C)
    {   
    for (int i = 2; i*i<= C; i++) 
    {   
        while (C % i == 0) 
        {
         System.out.print(i + " "); 
         C = C / i;
        }
    }
        return C;
    }
}

I need to find the smallest Factor but I'm not sure how to do it

Upvotes: 1

Views: 5704

Answers (4)

Alnitak
Alnitak

Reputation: 339856

The value you need to return is your i, not C.

You should work through possible values of i in your loop, and return that value when you find that C % i == 0.

Note that for efficiency you should test 2, 3, and then every odd number thereafter. There's no point testing (4, 6, 8, ...) if you already tested 2:

public static int smallestFactor(int C) {
    if (C % 2 == 0) return 2;  // C is even

    for (int i = 3; i * i <= C; i += 2) {
        if (C % i == 0) return i;  // odd factor found
    }

    return C;  // no factor found
}

In fact the most efficient algorithm would only test for prime factors, but I suspect that's beyond the scope of what you've been asked.

Upvotes: 0

Juvanis
Juvanis

Reputation: 25950

Handling all exceptional cases, try this code:

public static long smallestFactor(int x)
{
    if(x < 1)  return -1;
    if(x == 1) return  1;

    for(int i=2; i<=x; i++)
       if(x % i == 0) 
          return i;

    return -1; // To stop compiler's complaints.
}

Upvotes: 0

AJcodez
AJcodez

Reputation: 34186

Small changes to your code- you were close!

public class Factor {

    public static long smallestFactor(int C) {

        for (int i = 2; i*i<= C; i++) {   
            if (C % i == 0) return i;
        }
        return -1;
    }
}

Upvotes: 0

verdesmarald
verdesmarald

Reputation: 11866

You need to use if instead of while, and return i if you find it.

public static long smallestFactor(int C)
{
    for (int i = 2; i*i<= C; i++) 
    {   
        if (C % i == 0)
        {
            return i;
        }
    }

    return C;
}

There are other improvements you could make, but that should get you started.

Upvotes: 5

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