Refactor removeDuplicates from O(n²) to O(n) using a Set

Author: RomanSanaye

Sprint-1/JavaScript/removeDuplicates/removeDuplicates.mjs

@@ -1,36 +1,28 @@
 /**
  * Remove duplicate values from a sequence, preserving the order of the first occurrence of each value.
  *
- * Time Complexity:
- * Space Complexity:
- * Optimal Time Complexity:
+/**
+* Originally (nested loops):
+* Time Complexity: O(n²) - the outer loop runs n times and the inner loop
+*   scans uniqueItems, which can grow up to n items (about n(n - 1) / 2
+*   checks in the worst case, when all items are unique)
+* Space Complexity: O(n) - uniqueItems can hold up to n items
+* Optimal Time Complexity: O(n) - every item must be read at least once, and
+*   a Set gives O(1) average lookups
+
+* After refactor ([...new Set(inputSequence)]):
+* Time Complexity: O(n) - building the Set visits each item once with O(1)
+*   average inserts; spreading it into an array is also O(n)
+* Space Complexity: O(n) - the Set and the result array each hold up to n items
+* Optimal Time Complexity: O(n) - every item must be read at least once, so we
+*   can't do better than linear
+* /
+ * 
  *
  * @param {Array} inputSequence - Sequence to remove duplicates from
  * @returns {Array} New sequence with duplicates removed
  */
 export function removeDuplicates(inputSequence) {
-  const uniqueItems = [];
-
-  for (
-    let currentIndex = 0;
-    currentIndex < inputSequence.length;
-    currentIndex++
-  ) {
-    let isDuplicate = false;
-    for (
-      let compareIndex = 0;
-      compareIndex < uniqueItems.length;
-      compareIndex++
-    ) {
-      if (inputSequence[currentIndex] === uniqueItems[compareIndex]) {
-        isDuplicate = true;
-        break;
-      }
-    }
-    if (!isDuplicate) {
-      uniqueItems.push(inputSequence[currentIndex]);
-    }
-  }
-
-  return uniqueItems;
+  
+  return [... new Set(inputSequence)];
 }