Level 4: Data shaping · Exercise 60 of 76 · Free

All orderings of a list

A JavaScript exercise from Scriptdrill. Solve it with a code editor in your browser that runs your function against example and hidden tests, and it is checked the moment you submit.

The task

Return every ordering of `items` as an array of arrays. The items are all different. List the orderings in this order: first all that start with the first item, then all that start with the second item, and so on, with the same rule applied to the rest of each ordering. So `[1, 2, 3]` gives `[1,2,3]`, `[1,3,2]`, `[2,1,3]`, `[2,3,1]`, `[3,1,2]`, `[3,2,1]`. An empty array has exactly one ordering, the empty one, so the result is `[[]]`. Do not change `items`.

What this exercise teaches

Each call fixes one element and hands the rest to a smaller version of the same problem; the empty array is the base case and returns one empty ordering, so that there is something to build on. Going through the items by position, not by value, gives the required order without sorting.

A hint if you get stuck

Use recursion: for each position `i`, take `items[i]` as the first element and put it in front of every permutation of the remaining items. The permutations of an empty array are `[[]]`.