/****************************************************************************** * Compilation: javac Inverse.java * Execution: java Euclid a n * * Reads two command line parameters p and q and computes the a^-1 mod n * if it exists. * * % java Inverse 345454 2323351 * 103835 ******************************************************************************/ class Inverse { static int[] gcd(int p, int q) { if (q == 0) return new int[] { p, 1, 0 }; int[] vals = gcd(q, p % q); int d = vals[0]; int a = vals[2]; int b = vals[1] - (p / q) * vals[2]; return new int[] { d, a, b }; } static int inverse(int k, int n) { int[] vals = gcd(k, n); int d = vals[0]; int a = vals[1]; int b = vals[2]; if (d > 1) { StdOut.println("Inverse does not exist."); return 0; } if (a > 0) return a; return n + a; } public static void main(String[] args) { int k = Integer.parseInt(args[0]); int n = Integer.parseInt(args[1]); StdOut.println("k^-1 = " + inverse(k, n)); } }