2016 Update

Task/Amicable-pairs/Java/amicable-pairs.java

@@ -0,0 +1,27 @@
+import java.util.Map;
+import static java.util.function.Function.*;
+import static java.util.stream.Collectors.*;
+import static java.util.stream.LongStream.*;
+
+public class AmicablePairs {
+
+    public static void main(String[] args) {
+        final int limit = 20_000;
+
+        Map<Long, Long> map = rangeClosed(1, limit)
+                .parallel()
+                .boxed()
+                .collect(toMap(identity(), AmicablePairs::properDivsSum));
+
+        rangeClosed(1, limit)
+                .forEach(n -> {
+                    long m = map.get(n);
+                    if (m > n && m <= limit && map.get(m) == n)
+                        System.out.printf("%s %s %n", n, m);
+                });
+    }
+
+    public static Long properDivsSum(long n) {
+        return rangeClosed(1, (n + 1) / 2).filter(i -> n % i == 0).sum();
+    }
+}