• Repetition The value repeats itself like {1,1,2}
• Order depending on the usecase, {1,2} might not be the same as {2,1}
• Combination When the order doesn't matter, it is a Combination.
• Permutation When the order does matter it is a Permutation.

Misc

• Travelling Salesman Problem

tool

• https://www.statskingdom.com/combinations-calculator.html

courses

• Combinatorics Overview | Brilliant Math & Science Wiki

Sources

• https://itnext.io/permutations-combinations-algorithms-cheat-sheet-68c14879aba5
• https://github.com/trekhleb/javascript-algorithms/tree/master/src/algorithms/sets/combinations
• https://en.wikipedia.org/wiki/Heap%27s_algorithm https://www.geeksforgeeks.org/heaps-algorithm-for-generating-permutations/
• https://www.mathsisfun.com/combinatorics/combinations-permutations.html