Sets

Deduplication, membership checks, set operations

Sets give O(1) lookup and handle duplicates automatically. Often the fastest solution for 'have I seen this before?' in interviews.

Language:

Python

All languages — Basic operations

JavaScript

const seen = new Set();
const seen2 = new Set([1, 2, 3]);

seen.add(4);
seen.delete(2);

seen.has(3);               // true  — O(1)!
seen.has(99);              // false

seen.size;                 // Anzahl

TypeScript

const seen = new Set<number>();
const seen2 = new Set<number>([1, 2, 3]);

seen.add(4);
seen.delete(2);

seen.has(3);               // true
seen.size;

Java

Set<Integer> seen = new HashSet<>();
Set<Integer> seen2 = new HashSet<>(Arrays.asList(1, 2, 3));

seen.add(4);
seen.remove(2);

seen.contains(3);          // true
seen.size();               // Anzahl

// Go hat kein eingebautes Set — Map als Set:
seen := make(map[int]bool)
seen[1] = true
seen[2] = true

seen[3] = true             // hinzufügen
delete(seen, 2)            // entfernen

_, exists := seen[3]       // exists = true
// Oder kürzer:
if seen[99] { /* ... */ }  // false ohne Fehler

C++

unordered_set<int> seen;
unordered_set<int> seen2 = {1, 2, 3};

seen.insert(4);
seen.erase(2);

seen.count(3);             // 1 (vorhanden) oder 0
seen.find(3) != seen.end(); // true
seen.size();