Unique Array
Difficulty: Easy, Duration: 10 minutes, Languages: JS, TS, Author: Kiran Dash (opens in a new tab)
Question
Create a function uniqueArray, which can be used to create a new array with unique elements from an existing array.
Example
example.ts
uniqueArray([2, 1, 2]); // [2, 1]Launch exercise in editor (opens in a new tab)
Solution
Brute force with Array.prototype.indexOf()
solution.ts
export default function uniqueArray(input: Array<number>): Array<number> {
const uniqueElements = [];
for (let elem of input) {
if (uniqueElements.indexOf(elem) === -1) {
uniqueElements.push(elem);
}
}
return uniqueElements;
}Time Complexity: O(n^2) since Array.prototype.indexOf() is an O(n) operation
Brute force with Array.prototype.includes()
solution.ts
export default function uniqueArray(input: Array<number>): Array<number> {
const uniqueElements = [];
for (let elem of input) {
if (!uniqueElements.includes(elem)) {
uniqueElements.push(elem);
}
}
return uniqueElements;
}Time Complexity: O(n^2) since Array.prototype.includes() is an O(n) operation
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Tracking elements with Set 🔥
Instead of Array.prototype.includes(), we can use Set.prototype.has() to check for existence of an element with O(1) time complexity
solution.ts
export default function uniqueArray(input: Array<number>): Array<number> {
const uniqueElements = [];
const seenElements = new Set();
for (let elem of input) {
if (!seenElements.has(elem)) {
uniqueElements.push(elem);
seenElements.add(elem);
}
}
return uniqueElements;
}Time Complexity: O(n)
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Convert to Set and back to Array
solution.ts
export default function uniqueArray(input: Array<number>): Array<number> {
return Array.from(new Set(input));
}Time Complexity: O(n)
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