Data commit

Task/Square-free-integers/Java/square-free-integers.java

@@ -0,0 +1,69 @@
+import java.util.ArrayList;
+import java.util.List;
+
+public class SquareFree
+{
+    private static List<Long> sieve(long limit) {
+        List<Long> primes = new ArrayList<Long>();
+        primes.add(2L);
+        boolean[] c = new boolean[(int)limit + 1]; // composite = true
+        // no need to process even numbers > 2
+        long p = 3;
+        for (;;) {
+            long p2 = p * p;
+            if (p2 > limit) break;
+            for (long i = p2; i <= limit; i += 2 * p) c[(int)i] = true;
+            for (;;) {
+                p += 2;
+                if (!c[(int)p]) break;
+            }
+        }
+        for (long i = 3; i <= limit; i += 2) {
+            if (!c[(int)i]) primes.add(i);
+        }
+        return primes;
+    }
+
+    private static List<Long> squareFree(long from, long to) {
+        long limit = (long)Math.sqrt((double)to);
+        List<Long> primes = sieve(limit);
+        List<Long> results = new ArrayList<Long>();
+
+        outer: for (long i = from; i <= to; i++) {
+            for (long p : primes) {
+                long p2 = p * p;
+                if (p2 > i) break;
+                if (i % p2 == 0) continue outer;
+            }
+            results.add(i);
+        }
+        return results;
+    }
+
+    private final static long TRILLION = 1000000000000L;
+
+    public static void main(String[] args) {
+        System.out.println("Square-free integers from 1 to 145:");
+        List<Long> sf = squareFree(1, 145);
+        for (int i = 0; i < sf.size(); i++) {
+            if (i > 0 && i % 20 == 0) {
+                System.out.println();
+            }
+            System.out.printf("%4d", sf.get(i));
+        }
+
+        System.out.print("\n\nSquare-free integers");
+        System.out.printf(" from %d to %d:\n", TRILLION, TRILLION + 145);
+        sf = squareFree(TRILLION, TRILLION + 145);
+        for (int i = 0; i < sf.size(); i++) {
+            if (i > 0 && i % 5 == 0) System.out.println();
+            System.out.printf("%14d", sf.get(i));
+        }
+
+        System.out.println("\n\nNumber of square-free integers:\n");
+        long[] tos = {100, 1000, 10000, 100000, 1000000};
+        for (long to : tos) {
+            System.out.printf("  from %d to %d = %d\n", 1, to, squareFree(1, to).size());
+        }
+    }
+}