feat: Added Map Reduce Design Pattern (#3184)

* MapReduce design pattern added * Updated README.md * added module to parent pom
2026-05-14 22:58:36 +00:00 · 2025-02-22 13:08:05 -05:00
parent e17f138223
commit 6785b53b02
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+/*
+ * This project is licensed under the MIT license. Module model-view-viewmodel is using ZK framework licensed under LGPL (see lgpl-3.0.txt).
+ *
+ * The MIT License
+ * Copyright © 2014-2022 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+package com.iluwatar;
+
+import java.util.ArrayList;
+import java.util.Comparator;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+/**
+ * The Reducer class is responsible for aggregating word counts from the shuffled data.
+ */
+public class Reducer {
+  private Reducer() {
+    throw new UnsupportedOperationException("Reducer is a utility class and cannot be instantiated.");
+  }
+  /**
+   * Sums the occurrences of each word and sorts the results in descending order.
+   *
+   * @param grouped A map where keys are words and values are lists of their occurrences.
+   * @return A sorted list of word counts in descending order.
+   */
+  public static List<Map.Entry<String, Integer>> reduce(Map<String, List<Integer>> grouped) {
+    Map<String, Integer> reduced = new HashMap<>();
+    for (Map.Entry<String, List<Integer>> entry : grouped.entrySet()) {
+      reduced.put(entry.getKey(), entry.getValue().stream().mapToInt(Integer::intValue).sum());
+    }
+
+    List<Map.Entry<String, Integer>> result = new ArrayList<>(reduced.entrySet());
+    result.sort(Map.Entry.comparingByValue(Comparator.reverseOrder()));
+    return result;
+  }
+}