I've been working at a problem on FreeCodeCamp called "9 billion names of God the integer". (The specifics of the problem itself aren't germane to my question, but have a look at the link if you're interested.) Admittedly I wrestled with this problem for several days before giving up and googling the answer. The problem originally comes from Rosetta Code, and I set about reading the answer provided for JavaScript to make sure I understood how this problem could be solved.
As far as I can tell, it's making calculations via good old-fashioned for loops, and even though it was published with short, non-descriptive variable names, I think I could work my way through it. However, here is the part that's tripping me up (note that the code below is a cleaned-up reproduction of the Rosetta Code solution, which had a lot of unnecessary comments and a couple of typos):
(function() {
var cache = [
[1]
];
function cumu(n) {
var r, l, x, Aa, Mi;
for (l = cache.length; l < n + 1; l++) {
r = [0];
for (x = 1; x < l + 1; x++) {
r.push(r[r.length - 1] + (Aa = cache[l - x < 0 ? cache.length - (l - x) : l - x])[(Mi = Math.min(x, l - x)) < 0 ? Aa.length - Mi : Mi]);
}
cache.push(r);
}
return cache[n];
}
function row(n) {
var r = cumu(n),
leArray = [],
i;
for (i = 0; i < n; i++) {
leArray.push(r[i + 1] - r[i]);
}
return leArray;
}
console.log("Rows:");
for (iterator = 1; iterator < 12; iterator++) {
console.log(row(iterator));
}
console.log("Sums");
[23, 123, 1234].forEach(function(a) {
var s = cumu(a);
console.log(a, s[s.length - 1]);
});
})()
Specifically this line within cumu(n):
r.push(r[r.length - 1] + (Aa = cache[l - x < 0 ? cache.length - (l - x) : l - x])[(Mi = Math.min(x, l - x)) < 0 ? Aa.length - Mi : Mi]);
This push method has [square brackets] after it. What does that do? I know the purpose of brackets as they pertain to arrays and objects, but I can't find any documentation about this usage. Mind you, the script seems to work as intended regardless, with the result printing to the console as expected and no errors coming up.
