Data commit

Task/Unprimeable-numbers/Java/unprimeable-numbers.java

@@ -0,0 +1,95 @@
+public class UnprimeableNumbers {
+
+    private static int MAX = 10_000_000;
+    private static boolean[] primes = new boolean[MAX];
+
+    public static void main(String[] args) {
+        sieve();
+        System.out.println("First 35 unprimeable numbers:");
+        displayUnprimeableNumbers(35);
+        int n = 600;
+        System.out.printf("%nThe %dth unprimeable number = %,d%n%n", n, nthUnprimeableNumber(n));
+        int[] lowest = genLowest();
+        System.out.println("Least unprimeable number that ends in:");
+        for ( int i = 0 ; i <= 9 ; i++ ) {
+            System.out.printf(" %d is %,d%n", i, lowest[i]);
+        }
+    }
+
+    private static int[] genLowest() {
+        int[] lowest = new int[10];
+        int count = 0;
+        int test = 1;
+        while ( count < 10 ) {
+            test++;
+            if ( unPrimable(test) && lowest[test % 10] == 0 ) {
+                lowest[test % 10] = test;
+                count++;
+            }
+        }
+        return lowest;
+    }
+
+    private static int nthUnprimeableNumber(int maxCount) {
+        int test = 1;
+        int count = 0;
+        int result = 0;
+        while ( count < maxCount ) {
+            test++;
+            if ( unPrimable(test) ) {
+                count++;
+                result = test;
+            }
+        }
+        return result;
+    }
+
+    private static void displayUnprimeableNumbers(int maxCount) {
+        int test = 1;
+        int count = 0;
+        while ( count < maxCount ) {
+            test++;
+            if ( unPrimable(test) ) {
+                count++;
+                System.out.printf("%d ", test);
+            }
+        }
+        System.out.println();
+    }
+
+    private static boolean unPrimable(int test) {
+        if ( primes[test] ) {
+            return false;
+        }
+        String s = test + "";
+        for ( int i = 0 ; i < s.length() ; i++ ) {
+            for ( int j = 0 ; j <= 9 ; j++ ) {
+                if ( primes[Integer.parseInt(replace(s, i, j))] ) {
+                    return false;
+                }
+            }
+        }
+        return true;
+    }
+
+    private static String replace(String str, int position, int value) {
+        char[] sChar = str.toCharArray();
+        sChar[position] = (char) value;
+        return str.substring(0, position) + value + str.substring(position + 1);
+    }
+
+    private static final void sieve() {
+        //  primes
+        for ( int i = 2 ; i < MAX ; i++ ) {
+            primes[i] = true;
+        }
+        for ( int i = 2 ; i < MAX ; i++ ) {
+            if ( primes[i] ) {
+                for ( int j = 2*i ; j < MAX ; j += i ) {
+                    primes[j] = false;
+                }
+            }
+        }
+    }
+
+}