Taken from DailyCodingProblem

Using a functionrand7() that returns an integer from 1 to 7 (inclusive) with uniform probability, implement a function rand5() that returns an integer from 1 to 5 (inclusive).

Solution

This is the answer I came up with:

// typescript

function rand5(): number {
  return Math.ceil(Math.random() * 5)
}

This is a really simple question, and I didn’t feel satisfied so I also implemented a solution that returns a random (inclusive) integer but guarantees that the integer remains unique until the entire range is exhausted – that is, rand(10) below would never return a duplicate number until all numbers from 1 through 10 have also been previously returned.

const set = new Set()

function rand(_number: number): number {
  // If full (all numbers have been previously returned), clear the set
  if (set.size === _number) {
    set.clear()
  }

  let random = Math.ceil(Math.random() * _number)

  let regen = () => {
    random = Math.ceil(Math.random() * _number)
  }

  while (set.has(random)) {
    // Regenerate the random number if it's already in the set
    regen()
  }

  // Add the random number to the set before returning
  set.add(random)
  return random
}

Testing

Solution tested in REPL:

https://www.typescriptlang.org/play?#code/GYVwdgxgLglg9mABAJwIZgCYFYAUBKALkTBAFsAjAU2UQG8AoRFSqEZJAWVSgAsA6CJRgAbHF1580mOKXyIAVIix56AX3r1hLRDEQBeRAAZ6Adx4jKiHLoA8iAEyG8dRoggIAznC19hcAOY4Utj4KkwwANQRavRAA

Extended solution tested in REPL:

https://www.typescriptlang.org/play?#code/MYewdgzgLgBBCmsC8MzwO4wMqIBQEoAoQgMwFcxgoBLcGAJwEMwATXAfTDIFsAjeegC5UPfvXzCufATADehGDGokYuBFAB0EagC94MJIZidRA-HIWK4iDcAA28RvQKWAvsUUPYTViG4GYAFlGKAALW3hqO1xgsI0fFj8CGAAqYykxIksvBngAc3gwAOSkAD4LKwZmRP8UWPDgSOj6+Oqk8zSTaXE3Dxh0UKj9NRtQxghcBL98c3lK+nzCl0V3S3UNRhY2Ke4iRQWoMnoincJVnOoAgAZCAaHVS4AeGAAmK9nLUEgQBw07EDyk2quAAjO89koANSQs6EIA