main.js

var fs = require('fs'),
    path = require('path'),
    input = path.join(__dirname, 'input.txt');

fs.readFile(input, {encoding: 'utf-8'}, function(err, data) {
    findSleepyGuard(data.split('\r\n'));
});

var guardWhoSleepsMost;
var mostSlept = 0;
var mostSleptMinute = -1

function findSleepyGuard(arr) {
    var sortedArray = arr.sort();
    var guards = new Map();
    var currentGuard;

    sortedArray.forEach(entry => {
        if(entry[25] == "#") {
            currentGuard = entry.substr(26,4).trim()
        }

        if(entry[19] == 'f' || entry[19] == 'w') {
            var list = [];
            if(guards.has(currentGuard)) {
                list = list.concat(guards.get(currentGuard));
            }
            list.push(entry.substr(15,2));
            guards.set(currentGuard, list);
        }
    });

    findGuardWhoSleepsMost(guards);

    console.log("Guard " + guardWhoSleepsMost + " slept the most with " + mostSlept + " minutes, where the most slept minute was " + mostSleptMinute + " And the answer is " + mostSleptMinute*parseInt(guardWhoSleepsMost));
}

function findGuardWhoSleepsMost(guardMap) {
    guardMap.forEach((value, key) => {
        var timeSlept = 0;
        var sleepMinutes = [];
        for(var i = 0; i < value.length; i += 2) {
            timeSlept += value[i+1] - 1  - value[i];
            for(var j = value[i]; j < value[i+1] - 1; j++) {
                if(!sleepMinutes[j])
                    sleepMinutes[j] = 0;
                sleepMinutes[j]++;
            }
        }
        if(timeSlept >= mostSlept) {
            mostSlept = timeSlept;
            guardWhoSleepsMost = key;
            mostSleptMinute = max(sleepMinutes);
        }
    });
}

function max(arr) {
    var res = 0;
    var minute = -1;
    for(var i = 0; i < arr.length; i++) {
        if(!arr[i]) continue;
        if(arr[i] > res) { 
            res = arr[i];
            minute = i;
        }
    }
    
    return minute;
}