java: add «846. Hand of Straights»

Signed-off-by: Matej Focko <me@mfocko.xyz>

java/hand-of-straights.java

@@ -0,0 +1,34 @@
+import java.util.TreeMap;
+
+class Solution {
+  public boolean isNStraightHand(int[] hand, int groupSize) {
+    if (hand.length % groupSize != 0) {
+      return false;
+    }
+
+    TreeMap<Integer, Integer> cards = new TreeMap<>();
+    for (int card : hand) {
+      cards.compute(card, (c, present) -> 1 + ((present == null) ? 0 : present));
+    }
+
+    while (!cards.isEmpty()) {
+      int card = cards.entrySet().iterator().next().getKey();
+
+      for (int i = 0; i < groupSize; ++i) {
+        // card doesn't exist
+        if (!cards.containsKey(card + i)) {
+          return false;
+        }
+
+        cards.put(card + i, cards.get(card + i) - 1);
+
+        // remove entry of used cards
+        if (cards.get(card + i) == 0) {
+          cards.remove(card + i);
+        }
+      }
+    }
+
+    return true;
+  }
+}