[Hacker Rank] Interview Preparation Kit: Dictionaries and Hashmaps: Frequency Queries. Try to reduce complexity using OOP.

Author: Gonzalo Diaz

algorithm-exercises-java/src/main/java/ae/hackerrank/interview_preparation_kit/dictionaries_and_hashmaps/FrequencyQueries.java

@@ -24,83 +24,99 @@ private FrequencyQueries() {
   private static final int __NOT_FOUND__ = 0;
   private static final int __FOUND__ = 1;
 
+  Map<Long, Long> valueFreqs = new HashMap<>();
+  Map<Long, List<Long>> freqMap = new HashMap<>();
+  List<Integer> result = new ArrayList<>();
+
+  void insert(Long value) {
+    Long currentFreqCount = this.valueFreqs.getOrDefault(value, null);
+    Long newFreqCount;
+    List<Long> newFreq;
+
+    newFreqCount = (currentFreqCount == null ? __INITIAL__ : currentFreqCount + 1L);
+    valueFreqs.put(value, newFreqCount);
+
+    newFreq = freqMap.getOrDefault(newFreqCount, null);
+
+    // delete current frequency
+    if (currentFreqCount != null) {
+      freqMap.get(currentFreqCount).remove(value);
+      if (freqMap.get(currentFreqCount).isEmpty()) {
+        freqMap.remove(currentFreqCount);
+      }
+    }
+
+    // add new frequency
+    if (newFreq == null) {
+      newFreq = new ArrayList<>();
+      newFreq.add(value);
+      freqMap.put(newFreqCount, newFreq);
+    } else {
+      freqMap.get(newFreqCount).add(value);
+    }
+  }
+
+  void delete(Long value) {
+    Long currentFreqCount = this.valueFreqs.getOrDefault(value, null);
+    Long newFreqCount;
+    List<Long> newFreq;
+
+    newFreqCount = (currentFreqCount == null ? 0 : currentFreqCount - 1L);
+    if (newFreqCount > 0L) {
+      valueFreqs.put(value, newFreqCount);
+
+      newFreq = freqMap.getOrDefault(newFreqCount, null);
+      // add new frequency
+      if (newFreq == null) {
+        newFreq = new ArrayList<>();
+        newFreq.add(value);
+        freqMap.put(newFreqCount, newFreq);
+      } else {
+        freqMap.get(newFreqCount).add(value);
+      }
+    } else {
+      valueFreqs.remove(value);
+    }
+
+    // delete current frequency
+    if (currentFreqCount != null) {
+      freqMap.get(currentFreqCount).remove(value);
+      if (freqMap.get(currentFreqCount).isEmpty()) {
+        freqMap.remove(currentFreqCount);
+      }
+    }
+  }
+
   /**
    * FrequencyQueries.
    */
   static List<Integer> freqQuery(List<List<Integer>> queries) {
-    List<Integer> result = new ArrayList<>();
-    Map<Long, Long> valueFreqs = new HashMap<>();
-    Map<Long, List<Long>> freqMap = new HashMap<>();
+
+    FrequencyQueries fq = new FrequencyQueries();
+    fq.result = new ArrayList<>();
 
     for (List<Integer> query : queries) {
       int operation = query.get(0);
       long value = query.get(1);
 
-      Long currentFreqCount = valueFreqs.getOrDefault(value, null);
-      Long newFreqCount;
-      List<Long> newFreq;
-
       switch (operation) {
         case __INSERT__:
-          newFreqCount = (currentFreqCount == null ? __INITIAL__ : currentFreqCount + 1L);
-          valueFreqs.put(value, newFreqCount);
-
-          newFreq = freqMap.getOrDefault(newFreqCount, null);
-
-          // delete current frequency
-          if (currentFreqCount != null) {
-            freqMap.get(currentFreqCount).remove(value);
-            if (freqMap.get(currentFreqCount).isEmpty()) {
-              freqMap.remove(currentFreqCount);
-            }
-          }
-
-          // add new frequency
-          if (newFreq == null) {
-            newFreq = new ArrayList<>();
-            newFreq.add(value);
-            freqMap.put(newFreqCount, newFreq);
-          } else {
-            freqMap.get(newFreqCount).add(value);
-          }
+          fq.insert(value);
 
           break;
         case __DELETE__:
-          newFreqCount = (currentFreqCount == null ? 0 : currentFreqCount - 1L);
-          if (newFreqCount > 0L) {
-            valueFreqs.put(value, newFreqCount);
-
-            newFreq = freqMap.getOrDefault(newFreqCount, null);
-            // add new frequency
-            if (newFreq == null) {
-              newFreq = new ArrayList<>();
-              newFreq.add(value);
-              freqMap.put(newFreqCount, newFreq);
-            } else {
-              freqMap.get(newFreqCount).add(value);
-            }
-          } else {
-            valueFreqs.remove(value);
-          }
-
-          // delete current frequency
-          if (currentFreqCount != null) {
-            freqMap.get(currentFreqCount).remove(value);
-            if (freqMap.get(currentFreqCount).isEmpty()) {
-              freqMap.remove(currentFreqCount);
-            }
-          }
+          fq.delete(value);
 
           break;
         case __SELECT__:
-          result.add(freqMap.containsKey(value) ? __FOUND__ : __NOT_FOUND__);
+          fq.result.add(fq.freqMap.containsKey(value) ? __FOUND__ : __NOT_FOUND__);
           break;
         default:
           throw new IllegalArgumentException(
               "Operation %d not supported".formatted(operation));
       }
     }
 
-    return result;
+    return fq.result;
   }
 }