findcommonitems func complexity analysis + refactoring for better efficiency

Author: Mikiyas-STP

Sprint-1/JavaScript/findCommonItems/findCommonItems.js

@@ -9,6 +9,30 @@
  * @param {Array} secondArray - Second array to compare
  * @returns {Array} Array containing unique common items
  */
-export const findCommonItems = (firstArray, secondArray) => [
-  ...new Set(firstArray.filter((item) => secondArray.includes(item))),
-];
+// export const findCommonItems = (firstArray, secondArray) => [
+//   ...new Set(firstArray.filter((item) => secondArray.includes(item))),
+// ];
+// My analysis report
+// The function have a hidden nested loop using filter() and includes() This makes it quite expensive for us
+
+// Time Complexity
+// .filter() does n operation and .includes() does m operation since it is a nested loop the time complexity would be the product of the two complexities
+// O (n * m )
+// Space Complexity
+// .filter creates a temporary array to store common items O(n) space and "Set" also takes O(m) space. This is un avoidable if we use this nested loop
+
+// The inefficiency is on the hidden nested loop
+
+export const findCommonItems = (firstArray, secondArray) => {
+  const arraySet = new Set(secondArray);
+  const commonItems = firstArray.filter((item) => {
+    return arraySet.has(item);
+  });
+
+  return [...new Set(commonItems)];
+};
+
+
+// Time complexity is O(n + m) which is O(n) complexity from line 28 and o(m) complexity from line 32. i neglected line 27 complexity since it is O(1)
+// Space Complexity stays almost same
+// and we can say refactoring this code makes it fast.