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Sets

TypeScript has a built-in type for sets, which are collections of unique values. You can ensure that all the values in the set are of the same type by specifying a type parameter: <T>.

// A Set that contains only strings
const justiceLeague = new Set<string>();

justiceLeague.add("Green Arrow");
justiceLeague.add("Flash");

// Error: Argument of type '2' is not assignable to parameter of type 'string'
justiceLeague.add(2);

An array can be converted into a set, which automatically removes duplicate values:

// A Set automatically removes duplicate values from an array
const names = ["plasticman", "firestorm", "plasticman"];
const justiceLeague = new Set<string>(names);

console.log(justiceLeague);
// Set { 'plasticman', 'firestorm' }

Sets also have a few other interesting methods and properties:

const justiceLeague = new Set<string>(["Atom", "Black Canary", "Blue Beetle"]);

console.log(justiceLeague.size); // 3

justiceLeague.delete("Blue Beetle");
console.log(justiceLeague.has("Blue Beetle")); // false

justiceLeague.forEach((member) => console.log(member));
// Atom
// Black Canary

Assignment

Complete the findNumUniqueLabels function. It takes an array of strings and returns the number of unique values in the array.

Use a set to remove duplicates