I want to get all k-length strings from given list of characters. I already wrote recursive function and it works well. But my generator version doesn't work at all. How can I fix my second function? Many thanks.
// recursive version
function product_rec(arr, k) {
if (k == 1) return arr;
let res = [];
for (const elem of arr) {
for (const s of product_rec(arr, k - 1)) {
res.push(elem + s);
}
}
return res;
}
var p = product_rec(['0', '1'], 2);
console.log(p); // [ '00', '01', '10', '11' ]
// RangeError: Maximum call stack size exceeded
function* product_rec_gen(arr, k, result) {
if (k == 1) {
for (const elem of arr) yield elem;
}
for (const elem of arr) {
for (const s of product_rec_gen(arr, k - 1)) {
yield elem + s;
}
}
}
var p = product_rec_gen(['0', '1'], 2);
// RangeError: Maximum call stack size exceeded
for (const e of p){
console.log(e);
}
Iterate each element of the input array no matter it's length, handling the k==1 case inside the loop. Form the remainder array for each element and combine that element with the recursive call using that remainder...
function* product_rec(arr, k) {
for (let i = 0; i < arr.length; i++) {
if (k === 1) {
yield [arr[i]];
} else {
const rest = product_rec(arr.slice(i+1), k-1);
for (let el of rest) {
yield [arr[i], ...el];
}
}
}
}
const generator = product_rec(['a', 'b', 'c', 'd'], 2);
console.log(generator.next().value)
console.log(generator.next().value)
console.log(generator.next().value)
console.log(generator.next().value)
console.log(generator.next().value)
console.log(generator.next().value)