4kyu: add „Hamming Numbers“

Signed-off-by: Matej Focko <mfocko@redhat.com>

4kyu/hamming_numbers/solution.java

@@ -0,0 +1,26 @@
+import java.util.PriorityQueue;
+
+public class Hamming {
+    private static void update(PriorityQueue<Long> q, long n) {
+        q.add(2*n);
+        q.add(3*n);
+        q.add(5*n);
+    }
+
+    public static long hamming(int n) {
+        PriorityQueue<Long> cache = new PriorityQueue<>();
+        update(cache, 1);
+
+        long smallest = 1;
+        for (int i = 1; i < n; i++) {
+            smallest = cache.poll();
+            while (cache.peek() == smallest) {
+                cache.poll();
+            }
+
+            update(cache, smallest);
+        }
+
+        return smallest;
+    }
+}

README.md

@@ -56,6 +56,7 @@
 ### Java
 
 - [Sum of Intervals](https://www.codewars.com/kata/52b7ed099cdc285c300001cd) - [solution](4kyu/sum_of_intervals)
+- [Hamming Numbers](https://www.codewars.com/kata/526d84b98f428f14a60008da) - [solution](4kyu/hamming_numbers)
 
 ## 5 kyu