top k freq solution

Author: nancyel

top-k-frequent-elements/nancyel.ts

@@ -0,0 +1,21 @@
+/**
+ * time complexity: O(n + m log m),
+ *   n = length of input array
+ *   m = number of unique elements (m ≤ n)
+ * space complexity: O(m)
+ */
+
+function topKFrequent(nums: number[], k: number): number[] {
+  const freqMap = new Map<number, number>();
+
+  // Count frequencies using a map: O(n)
+  for (const num of nums) {
+    freqMap.set(num, (freqMap.get(num) || 0) + 1);
+  }
+
+  // Extract the top k elements
+  return Array.from(freqMap.entries()) // O(m)
+    .sort(([, a], [, b]) => b - a) // O(m log m)
+    .slice(0, k)
+    .map(([num]) => num); // extract the keys only
+}