1. Dedup with Set
Passing an array to new Set drops duplicates, keeping each value once.
new Set([1, 2, 2, 3])Typorithm · medium
Set
set-operationscollectionssetdedupmembership
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Full lesson · 8 learning steps Open any exercise for focused practice
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Step 1 of 8 · intro card
Learn Set
Objects & Maps
A Set stores unique values: new Set(arr) deduplicates, has gives O(1) membership, and add/delete mutate it. Spread back to an array with [...s], and build union and intersection with spread and filter.
A Set holds each value at most once, so new Set(array) is the idiomatic one-liner for removing duplicates.
Membership with set.has(x) is O(1), far faster than array.includes on large data, and add/delete keep the Set up to date.
Sets are not arrays — spread with [...set] to get an array back — and you compose them: union is new Set([...a, ...b]) while intersection is new Set([...a].filter((x) => b.has(x))).
01
new Set(arr) deduplicates values.
02
has, add, and delete are O(1) operations.
03
Spread + filter build union and intersection.
const unique = new Set([1, 2, 2, 3])
const present = unique.has(2)
unique.add(4)
unique.delete(1)
const arr = [...unique]
const a = new Set([1, 2, 3])
const b = new Set([2, 3, 4])
const union = new Set([...a, ...b])
const intersection = new Set([...a].filter((x) => b.has(x)))Read the implementation
Connect each part of the code to the concept before you type.
2. Membership test
has(value) is an O(1) check for whether the value is in the Set.
unique.has(2)3. add a value
add inserts a value; adding an existing value is a no-op.
unique.add(4)4. delete a value
delete removes a value and returns whether it was present.
unique.delete(1)5. Back to array
Spreading a Set into an array is the standard way to materialize its values.
[...unique]6. Union
Spreading both Sets into one new Set yields their union with duplicates removed.
new Set([...a, ...b])7. Intersection
Filtering a's values by b.has keeps only the values present in both Sets.
new Set([...a].filter((x) => b.has(x)))A complete learning loop
01
Understand
Read the concept map and follow the code breakdown.
02
Reconstruct
Type the implementation, repair mistakes and work through every recall exercise.
03
Verify
Use the final check without hints; revisit weak concepts in short practice sessions.