Appear only once

Disclosure

Most of the problems under my TypeHero Challenges folder were either obtained from typehero.dev or from type-challenges repo. Purpose of these articles are just to document my approaches for my easy reference. Please visit the respective links for more info.

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Problem Description

Find the elements in the target array that appear only once. For example：input: [1,2,2,3,3,4,5,6,6,6]，ouput: [1,4,5].

Solutions

Approach 1: Loose equals

type Includes<Haystack extends any[], Needle> = Needle extends Haystack[number] ? true : false;
 
type FindEles<Suffix extends any[], Prefix extends any[] = [], Result extends any[] = []> =
	Suffix extends [infer First, ...infer Rest]
	?	Includes<[...Prefix, ...Rest], First> extends false
		? FindEles<Rest, [...Prefix, First], [...Result, First]>
		: FindEles<Rest, [...Prefix, First], Result>
	: Result;

Approach 2: Strict equals (Handles objects)

// type Equal = /* ... */
 
type IncludesStrict<Haystack extends any[], Needle> = Haystack extends [infer First, ...infer Rest]
	? Equal<First, Needle> extends true
		? true
		: IncludesStrict<Rest, Needle>
	: false
 
type FindEles<Suffix extends any[], Prefix extends any[] = [], Result extends any[] = []> =
	Suffix extends [infer First, ...infer Rest]
	?	IncludesStrict<[...Prefix, ...Rest], First> extends false
		? FindEles<Rest, [...Prefix, First], [...Result, First]>
		: FindEles<Rest, [...Prefix, First], Result>
	: Result;

TODO: There are more approaches to solving this in the Solutions tab.