java: add «884. Uncommon Words from Two Sentences»

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

java/uncommon-words-from-two-sentences.java

@@ -0,0 +1,27 @@
+import java.util.ArrayList;
+import java.util.HashMap;
+
+class Solution {
+  public String[] uncommonFromSentences(String s1, String s2) {
+    var counters = new HashMap<String, Integer>();
+
+    for (String word : s1.strip().split("\\s+")) {
+      counters.compute(word, (key, count) -> 1 + (count != null ? count : 0));
+    }
+
+    for (String word : s2.strip().split("\\s+")) {
+      counters.compute(word, (key, count) -> 1 + (count != null ? count : 0));
+    }
+
+    var uncommon = new ArrayList<String>();
+    for (var entry : counters.entrySet()) {
+      if (entry.getValue() != 1) {
+        continue;
+      }
+
+      uncommon.add(entry.getKey());
+    }
+
+    return uncommon.toArray(new String[0]);
+  }
+}