add: DaleStudy#347 top k frequent elements

Author: sukyoungshin

top-k-frequent-elements/suKyoung.ts

@@ -0,0 +1,105 @@
+// 1번풀이 (brute force)
+type FrequencyMap = Record<number, number>;
+
+function topKFrequentCountDown(nums: number[], k: number): number[] {
+  const freqMap = buildFrequencyMap1(nums);
+  return pickTopKDescending(freqMap, k);
+}
+
+function buildFrequencyMap1(nums: number[]): FrequencyMap {
+  const map: FrequencyMap = {};
+  for (const num of nums) {
+    map[num] = (map[num] || 0) + 1;
+  }
+  return map;
+}
+
+function pickTopKDescending(freqMap: FrequencyMap, k: number): number[] {
+  const result: number[] = [];
+  const entries = Object.entries(freqMap).map(([key, value]) => [
+    Number(key),
+    value,
+  ]);
+  let currentFrequent = Math.max(...entries.map(([_, freq]) => freq));
+
+  while (result.length < k && currentFrequent > 0) {
+    for (const [num, freq] of entries) {
+      if (freq === currentFrequent) {
+        result.push(num);
+        if (result.length === k) break;
+      }
+    }
+    currentFrequent--;
+  }
+
+  return result;
+}
+
+
+// 2번풀이(Bucket Sort)
+function topKFrequent(nums: number[], k: number): number[] {
+    const frequencyMap = buildFrequencyMap2(nums);
+    const frequencyBuckets = buildFrequencyBuckets(nums.length, frequencyMap);
+
+    return collectTopKFrequent(frequencyBuckets, k);
+  }
+  
+  function buildFrequencyMap2(nums: number[]): FrequencyMap {
+    const freqMap: FrequencyMap = {};
+    for (const num of nums) {
+      freqMap[num] = (freqMap[num] || 0) + 1;
+    }
+    return freqMap;
+  }
+  
+  function buildFrequencyBuckets(
+    size: number,
+    freqMap: FrequencyMap
+  ): number[][] {
+    const buckets: number[][] = Array(size + 1).fill(null).map(() => []);
+  
+    for (const [numStr, frequent] of Object.entries(freqMap)) {
+      const num = Number(numStr);
+      buckets[frequent].push(num);
+    }
+  
+    return buckets;
+  }
+  
+  function collectTopKFrequent(buckets: number[][], k: number): number[] {
+    const result: number[] = [];
+  
+    for (let i = buckets.length - 1; i >= 0 && result.length < k; i--) {
+      for (const num of buckets[i]) {
+        result.push(num);
+        if (result.length === k) break;
+      }
+    }
+  
+    return result;
+  }
+  
+
+// 3번풀이 (MinHeap)
+function topKFrequentHeap(nums: number[], k: number): number[] {
+    const freqMap: Record<number, number> = {};
+  
+    for (const num of nums) {
+      freqMap[num] = (freqMap[num] || 0) + 1;
+    }
+  
+    const heap: [number, number][] = [];  
+    for (const [numStr, frequent] of Object.entries(freqMap)) {
+      const num = Number(numStr);
+  
+      heap.push([num, frequent]);
+      heap.sort((a, b) => a[1] - b[1]);
+
+      if (heap.length > k) {
+        heap.shift();
+      }
+    }
+  
+    return heap.map(([num]) => num);
+  }
+