CODEWITHSUNDEEP
javaalgorithmfunctionmathdouble
Rohit
Rohit

Reputation: 402

next multiple of a number to given multiplier

I want to write a function to find the next multiple of a number given a multiplier. Both the source number and multiplier could be floating point.

expected:

nextMult(3.654,0.5) = 4.0
nextMult(3.165,0.15) = 3.30
nextMult(3.452,0.002) = 3.452
nextMult(2, 0.3) = 2.1
nextMult(2, 0.2) = 2
nextMult(4, 3) = 6

My current solution:

public double nextMult(double source, double multiplier)
{
    for (double i = (double)((long)source - multiplier); i <= source + multiplier; 
        i += multiplier) 
    {
        if (i >= source) 
            return i;
    }
}

I don't like the multiple castings. Are there more efficient ways or existing library solutions that can do this?

Upvotes: 3

Views: 1284

Answers (2)

przemek hertel
przemek hertel

Reputation: 4024

both source and multiplier are of type: double

double result = Math.ceil(source/multiplier) * multiplier;

This works for all your test cases...

Upvotes: 1

Compass
Compass

Reputation: 5937

Yes there is. Since you've provided a working solution, you will notice that you've presented an O(n) solution that goes through a set number of operations and appears to increment until you've found it. This becomes terrifying when you do nextMult(10000000000000, 1); We'd be here all day iterating through that loop by hand.

However, there is actually an O(1) solution.

int multiple = (int) (source / multiplier); //we get the whole number portion of the divided value, i.e. 4/3 = 1, 3.654/0.5 = 7
double remainder = source % multiplier; //we need to check for if it matches the higher
if(remainder > 0) {
    multiple++; // and we want the next higher one
}
return multiplier * multiple;

That being said, this only handles POSITIVE values. I will leave handling the negative values up to you as an exercise.

Edit: You will need to implement BigDoubles for modulus. Doubles and modulus apparently hate each other.

Upvotes: 2

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