AllCombinationsOfSizeK.js

/*
 Problem: Given two numbers, n and k, make all unique combinations of k numbers from 1 to n and in sorted order

 What is combinations?
 - Combinations is selecting items from a collections without considering order of selection

 Example:
 - We have an apple, a banana, and a jackfruit
 - We have three objects, and need to choose two items, then combinations will be

 1. Apple & Banana
 2. Apple & Jackfruit
 3. Banana & Jackfruit

 To read more about combinations, you can visit the following link:
 - https://betterexplained.com/articles/easy-permutations-and-combinations/

 Solution:
 - We will be using backtracking to solve this questions
 - Take one element, and make all them combinations for k-1 elements
 - Once we get all combinations of that element, pop it and do same for next element
*/

class Combinations {
 constructor (n, k) {
 this.n = n
 this.k = k
 this.current = [] // will be used for storing current combination
 this.combinations = []
 }

 findCombinations (high = this.n, total = this.k, low = 1) {
 if (total === 0) {
 this.combinations.push([...this.current])
 return this.combinations
 }
 for (let i = low; i <= high; i++) {
 this.current.push(i)
 this.findCombinations(high, total - 1, i + 1)
 this.current.pop()
 }
 return this.combinations
 }
}

export { Combinations }