我该如何处理非负模型？

Question

When I use the operator % in my Java programs, I keep getting negative answers. Example: -1%100 gives -1. While this is mathematically correct, I want to get the normal mathematical solution, or 99. In other words, I want to get the smallest positive integer solution. Is there any simple solution for this in Java (perhaps something I overlooked in Math? -- I can't find it)?

I also want to clarify that if there is something in the API that does this, a link would be awesome.

Answer 1

You can just do this?

int d = 100;

int x = -1 % d;
if (x < 0)
    x += d;

This should work for any positive d .

Answer 2

You can do the following

int myMod(int x, int modulo)
{
   return ((x % modulo) + modulo)  % modulo
}

Answer 3

This works, for any values in place of d or x.

int d=100;
int x=-1%d;
while (x<0)
    x+=d;

Answer 4

i < 0 ? n - ((-i - 1) % n + 1) : i % n

For example:

class Mod {
  public static int mod(int i, int n) {
    return i < 0 ? n - ((-i - 1) % n + 1) : i % n;
  }

  public static void main(String [] args) {
    System.out.println("mod(-201, 100) == " + mod(-201, 100));
    System.out.println("mod(-200, 100) == " + mod(-200, 100));
    System.out.println("mod(17, 100) == " + mod(17, 100));
    System.out.println("mod(100, 100) == " + mod(100, 100));
  }
}

And

$ javac Mod.java && java Mod
mod(-201, 100) == 99
mod(-200, 100) == 0
mod(17, 100) == 17
mod(100, 100) == 0

No loops.