二刷347，尝试桶排序

Author: diguage

docs/0347-top-k-frequent-elements.adoc

@@ -56,6 +56,15 @@ include::{sourcedir}/_0347_TopKFrequentElements.java[tag=answer]
 include::{sourcedir}/_0347_TopKFrequentElements_2.java[tag=answer]
 ----
 --
+
+二刷（桶排序）::
++
+--
+[{java_src_attr}]
+----
+include::{sourcedir}/_0347_TopKFrequentElements_21.java[tag=answer]
+----
+--
 ====
 
 

logbook/202503.adoc

@@ -68,7 +68,7 @@ endif::[]
 |{counter:codes2503}
 |{leetcode_base_url}/top-k-frequent-elements/[347. Top K Frequent Elements^]
 |{doc_base_url}/0347-top-k-frequent-elements.adoc[题解]
-|✅ Top K 问题，优先队列
+|✅ Top K 问题，优先队列；桶排序
 
 |===
 

src/main/java/com/diguage/algo/leetcode/_0347_TopKFrequentElements_21.java

@@ -0,0 +1,48 @@
+package com.diguage.algo.leetcode;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+public class _0347_TopKFrequentElements_21 {
+  // tag::answer[]
+  /**
+   * 桶排序
+   *
+   * @author D瓜哥 · https://www.diguage.com
+   * @since 2025-03-26 14:56:31
+   */
+  public int[] topKFrequent(int[] nums, int k) {
+    Map<Integer, Integer> numToCountMap = new HashMap<>();
+    int maxCount = 0;
+    for (int num : nums) {
+      Integer count = numToCountMap.getOrDefault(num, 0);
+      Integer newCnt = ++count;
+      if (newCnt > maxCount) {
+        maxCount = newCnt;
+      }
+      numToCountMap.put(num, newCnt);
+    }
+    List<Integer>[] buckets = new ArrayList[maxCount + 1];
+    numToCountMap.forEach((key, v) -> {
+      if (buckets[v] == null) {
+        buckets[v] = new ArrayList<>();
+      }
+      buckets[v].add(key);
+    });
+    int[] result = new int[k];
+    for (int i = maxCount; i >= 0 && k > 0; i--) {
+      if (buckets[i] != null) {
+        for (int num : buckets[i]) {
+          result[--k] = num;
+        }
+      }
+    }
+    return result;
+  }
+  // end::answer[]
+  public static void main(String[] args) {
+    new _0347_TopKFrequentElements_21().topKFrequent(new int[]{4, 1, -1, 2, -1, 2, 3}, 2);
+  }
+}