In trying to solve the following problem:
Generate all combinations of an array of string. Ex: Input: ['A', 'T', 'C', 'K'] Output: [ 'ATCK', 'ATC', 'ATK', 'AT', 'ACK', 'AC', 'AK', 'A', 'TCK', 'TC', 'TK', 'T', 'CK', 'C', 'K', '' ] I have the following code:
function getSpellableWords(arr) { const res = []; // helper(arr, res, 0, ''); helper(arr, res, 0, []); return res; } function helper(arr, res, i, slate) { const char = arr[i]; console.log(i, 'i') if(i === arr.length) { res.push(slate.join('')); return; } // slate = slate + char; slate.push(char) console.log(slate, 'slate') helper(arr, res, i+1, slate); slate.pop() helper(arr, res, i+1, slate); } getSpellableWords(['A', 'T', 'C', 'K']); My questions is:
If I remove the following lines in the code:
helper(arr, res, i+1, slate); Once i is equal to 5 (which is the array.length), the code will stop after it pushes slate into res. However, if I leave that line in, a call stack is set up and so i will go up from 1->5, then pop out gradually to 4 then 3 then back to 4 and so on. Why does that happen?
Clarification: So I understand that for each recursion call, another i variable is generated. However, I was expecting the second recursion call to also generate i from 1->4 again, but this time instead of incrementing it linearly, there's backtracking going on as well. Why wasn't there backtracking in the first call, and why does the second call generate the rest of the results when the first call only generates the first result?