Java program to display factors of a number?

Answer 1

One solution is to use a for-loop counting from 1 to half of the number. If the modulus of the number and the current value in the loop is zero, the current value is a factor of the number. The number divided by the current value is also a factor.

Answer 2

for (int i = 1; i <= number; i++) { if (number % i == 0) { System.out.println(i); } }

The above displays all the factors of a number. Prime factorization is a little more complicated (every time you find a factor, display it, then divide the number by this factor before you continue).

Here's a more efficient approach... once you know you have a factor, you don't have to look above it. For example with a test number like 10000, you know 2 is a factor (paired with 5000), thus there is no need to test above 5000.

public static int[] GetFactors(int nInput)

{

int nNumberToFactor = nInput;

int nCurrentUpper = nInput;

int i;

List<int> factors = new List<int>();

factors.Add(1);

for (i = 2; i < nCurrentUpper; i++)

{

if ((nNumberToFactor % i) == 0)

{

// if we found a factor, the upper number is the new upper limit

nCurrentUpper = nNumberToFactor / i;

factors.Add(i);

if (nCurrentUpper != i) // avoid "double counting" the square root

factors.Add(nCurrentUpper);

}

}

factors.Sort();

return factors.ToArray();

}