Find maximum possible time HH:MM by permuting four given digits

Question

I recently took a coding test for a promotion at work. This was one of the tasks I really struggled with and was wondering what is the best way to do this. I used a load of

Answer 1

Really late for the party, but I think there a quite straightforward solution to the problem (slower and uglier than other solutions, though). Just iterate (no hardcoding, no permutations) through all integer values from 2359 to 0 and check if they contain provided digits:

Number.prototype.pad = function(size) {
    var s = String(this);
    while (s.length < (size || 2)) {s = "0" + s;}
    return s;
}

getHHMM = (val) => `${Math.floor(val / 100).pad(2)}:${(val % 100).pad(2)}`;

isValidDate = value => !isNaN(new Date(`1970-01-01T${getHHMM(value)}`).getTime());

isFit = function(a, b, c, d, value) {
    var valStr = value.pad(4).split("").sort().join("");
    var digStr = [a, b, c, d].sort().join("");
    return valStr === digStr;
}

generate = function(a, b, c, d) {
    for (var i = 2359; i >= 0; i--) {
        if (isFit(a, b, c, d, i) && isValidDate(i))
            return getHHMM(i);
    }
    return "NOT POSSIBLE";
}