Initial data commit

Task/Totient-function/Java/totient-function.java

@@ -0,0 +1,41 @@
+public class TotientFunction {
+
+    public static void main(String[] args) {
+        computePhi();
+        System.out.println("Compute and display phi for the first 25 integers.");
+        System.out.printf("n  Phi  IsPrime%n");
+        for ( int n = 1 ; n <= 25 ; n++ ) {
+            System.out.printf("%2d  %2d  %b%n", n, phi[n], (phi[n] == n-1));
+        }
+        for ( int i = 2 ; i < 8 ; i++ ) {
+            int max = (int) Math.pow(10, i);
+            System.out.printf("The count of the primes up to %,10d = %d%n", max, countPrimes(1, max));
+        }
+    }
+
+    private static int countPrimes(int min, int max) {
+        int count = 0;
+        for ( int i = min ; i <= max ; i++ ) {
+            if ( phi[i] == i-1 ) {
+                count++;
+            }
+        }
+        return count;
+    }
+
+    private static final int max = 10000000;
+    private static final int[] phi = new int[max+1];
+
+    private static final void computePhi() {
+        for ( int i = 1 ; i <= max ; i++ ) {
+            phi[i] = i;
+        }
+        for ( int i = 2 ; i <= max ; i++ ) {
+            if (phi[i] < i) continue;
+            for ( int j = i ; j <= max ; j += i ) {
+                phi[j] -= phi[j] / i;
+            }
+        }
+    }
+
+}