How can I make a search function using regEx? I have some code but can't post it at the moment due to my computer being very broken and annoying, I will try again tomorrow!
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My approach is to put a second function inside the main public API that has whatever additional arguments needed. From the outside, that's invisible, but it lets you write the actual function that does the work without concern for an ugly API.Pointy– Pointy2019-12-16 22:19:37 +00:00Commented Dec 16, 2019 at 22:19
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2 Answers
This is not really what would be called combinations, but permutations.
The idea is to use recursion for getting the result for a shorter array, i.e. the one that lacks the first element.
Then take all permutations you get back from the recursive call, and insert the left-out value in each possible index.
When input has duplicates, then you need to stop inserting the left-out value as soon as you find that same value preceding the insertion spot.
Here is how that looks:
function scramble(array) {
if (array.length == 0) {
return [[]];
}
let results = [];
// solve the problem for a shorter array (first value excluded), and iterate:
for (let perm of scramble(array.slice(1))) {
// add the missing element in each possible position:
for (let i = 0; i < array.length; i++) {
// next IF is only needed when input has duplicates, and
// output should not repeat same array:
if (i && array[0] === perm[i-1]) break;
results.push(perm.slice(0, i).concat(array[0], perm.slice(i)));
}
}
return results;
}
let array = ["I", "am", "coding", "am"];
console.log(scramble(array));Without the inner if, an input with duplicate values will produce duplicate arrays. If this is not desired, then the if is needed.
3 Comments
ssbarbee
I got stuck on the same values. Any way to resolve that?
trincot
Yes, break out of the inner loop when you pass over the same value as the one you want to insert. See update to my answer.
You could iterate and get a flat array of the mapping of the value with the result of the nested calls.
function permutation(array) {
return array.length === 1
? [array]
: array.flatMap((v, i) => permutation([
...array.slice(0, i),
...array.slice(i + 1)
]).map(a => [v, ...a]));
}
permutation(["I", "am", "coding"]).map(a => console.log(...a));