Exercise 1: Remove Duplicates (keep order)

Name: Karmyug Techzone
Address: 2nd Floor, Karuba Tower, 80 Feet Road, Ratlam, Madhya Pradesh, 457001, IN
Telephone: +91-8962241437
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Problem Statement

Create a function `unique(arr)` that removes duplicates but preserves original order.

Sample Output:

unique([1, 2, 2, 3, 1, 4]) => [1, 2, 3, 4]
unique(["a", "b", "a", "c"]) => ["a", "b", "c"]

Solution

const unique = (arr) => {
  const seen = new Set();
  return arr.filter((x) => (seen.has(x) ? false : (seen.add(x), true)));
};

Explanation

Line 1: function header

const unique = (arr) => { → ek arrow function bana rahe hain jiska naam unique hai.
arr parameter hai: ye wahi input array hoga jisme duplicates ho sakte hain.

Line 2: Set kyu?

const seen = new Set(); → yaha Set ek special data structure hai jisme values unique hoti hain.
Har value sirf 1 baar store hoti hai, isliye “already dekha hai kya?” check karna super fast ho jata hai.

Line 3: filter ke andar logic

return arr.filter((x) => (...)) → filter har element x ko check karega.
seen.has(x) → puch raha hai: kya ye value pehle se seen me hai?
Agar seen.has(x) true hai → iska matlab ye duplicate hai → false return, to ye element naya array me nahi aayega.
Agar seen.has(x) false hai → to hum (seen.add(x), true) chala rahe hain:
seen.add(x) → pehli baar is value ko seen me store karo.
, true (comma operator) → last expression true return karta hai, to filter ko true milta hai.
true ka matlab: ye element new array me include karo.

Result:

Pehli baar aane wali har value add hogi, duplicates skip ho jayenge.
Original order bhi same rahega kyunki hum sirf skip kar rahe hain, re‑order nahi.

Real world:

Tags list, selected filters, recently viewed products jaha duplicate entries nahi chahiye.

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Exercise 1: Remove Duplicates (keep order)

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