problem1.js

const openingHours = {
  monday: [
    { begin: '10:00', end: '12:00' },
    { begin: '13:00', end: '18:00' },
  ],
  tuesday: [
    { begin: '10:00', end: '12:00' },
    { begin: '13:00', end: '18:00' },
  ],
  wednesday: [
    { begin: '10:00', end: '12:00' },
    { begin: '13:00', end: '18:00' },
  ],
  thursday: [
    { begin: '10:00', end: '12:00' },
    { begin: '13:00', end: '18:00' },
  ],
  friday: [],
  saturday: [],
  sunday: [],
}

const weekDays = [ 'monday', 'tuesday', 'wednesday', 'thursday', 'friday', 'saturday', 'sunday' ]


const toMinutes = h => {
  const [ hours, minutes ] = h.split(':').map(Number)

  return hours * 60 + minutes
}

console.log(toMinutes('00:23')) // 23
console.log(toMinutes('01:23')) // 83
console.log(toMinutes('02:00')) // 120

const addHours = (newHours, toDays) => {
  const days = Object.keys(daysSelected)
    .filter(key => daysSelected[key] === true)

  // Improve2. check for collision
  for (const day of days) {
    const dayHours = openingHours[day]

    for (hours of dayHours) {
      const b1 = toMinutes(newHours.begin)
      const b2 = toMinutes(hours.begin)

      const e1 = toMinutes(newHours.end)
      const e2 = toMinutes(hours.end)

      // if collides -> return
      if ((b1 >= b2 && b1 < e2) || (e1 > b2 && e1 <= e2)) {
        console.error(newHours, 'collides with', hours)
        return
      }
    }
  }

  // add
  for (const day of days) {
    const dayHours = openingHours[day]
    dayHours.push(newHours)

    // Improve1. sort
    dayHours.sort((a, b) => b.begin < a.begin)
  }

}

// Tests

const daysSelected = { // should be called 'selectedDays'
  monday: true,
  tuesday: true,
  wednesday: true,
  thursday: true,
  friday: false,
  saturday: false,
  sunday: false,
}

console.log(openingHours)

addHours({ begin: '06:00', end: '09:00' }, daysSelected)
addHours({ begin: '05:00', end: '06:00' }, daysSelected)
addHours({ begin: '11:00', end: '13:00' }, daysSelected) // collides
addHours({ begin: '07:00', end: '08:00' }, daysSelected) // collides
addHours({ begin: '18:00', end: '20:00' }, daysSelected)
addHours({ begin: '17:00', end: '20:00' }, daysSelected) // collides
addHours({ begin: '22:00', end: '02:00' }, daysSelected)

console.log(openingHours)

problem2.js

const cubes = n => n**3 - (n-2)**3

problem3.js

const print = (n = 1, count = 1) => {
  // limit
  if (count > 10) return

  let i = 0
  const a = []
  while (i < count) {
    a.push(n + i)
    i++
  }
  console.log(a.join(' '))
  print(n + i, count + 1)
}

print()