Javascript NodeJS ES6 combination/permutations algorithm

问题

Little challenge.

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Goal (nodeJS, loop is an * interator function using "yield" strategy)

var str;
var minChars = 1;
var maxChars = 10;
for (str of loop('abcdefghijklmnopqrstuvwxyz',minChars,maxChars)) {
    console.log(str);
}

---

Constraints:

• Only generate string combinations length between minChars and maxChars
• Must not consumme all memory (Array in store not allowed)
• Must use ES6 iterators, so step by step is possible
• Recursion is allowed
• Can provide billions of combination

---

Sample output (order is important):

a
b
c
[...]
z
aa
ab
ac
[...]
aaa
aab
aac
[...]
aba
abb
abc
[...]
bza
bzb
bzc
[...]
zzzzzzzzzz

回答1:

Trivial solution:

function* loop(alphabet, min, max) {
    if (min > max) throw new RangeError("max needs to be greater than min");
    if (min <= 0)
        yield "";
    if (max > 0)
        for (const rest of loop(alphabet, min-1, max-1))
            for (const a of alphabet)
                yield rest+a;
}

(Babel demo)

来源：https://stackoverflow.com/questions/34163786/javascript-nodejs-es6-combination-permutations-algorithm