Daily Challenge #153 - Horse Race Gamble

Setup

Your friend likes to go to the horse races and gamble on which horses will finish first, second, and third place. Unfortunately, he doesn't know how many horses will be entering until he gets to the track.

Write a function that will take any number of horses as its only argument. This function must return the total number of different combinations of winners for the gold, silver, and bronze medals.

For example, if there are 15 horses, there are 2730 possible unique combinations of winners. If the number of horses is 3 or less, return the input value. If the number of horses is not an integer, return undefined.

Examples

horses(15), 2730, true)
horses(2.5), undefined, false)

Tests

horses(12)
horses(2)
horses(11)
horses(a)

Good luck!

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Comments

[Rashmin Dandekar]

Ruby

def horses(num)
  if !(num % 1 == 0) || !(num.is_a? Numeric)
    return "undefined"
  elsif num < 3
    return num
  else
    return num*(num-1)*(num-2)
  end
end

puts horses(12)
puts horses(2)
puts horses(11)
puts horses(2.5)
puts horses("a")

[Nick Holmes]

Yes, I said that in my post.

However, I misread the challenge, and thought that "undefined" should be returned when n <= 3, although it should actually return the input.

[Nicholas Saccente]

Here's my submission while I'm learning Nim.

proc fac(n: int): int =
  if n <= 1: return 1
  result = n * fac(n - 1)

proc nPr(n: int, r: int): int =
  result = fac(n) div fac(n-r)

proc `%`(n: int, r: int): int =
  result = nPr(n, r)

proc horses(n: int): int =
  if n <= 3: return n
  result = n % 3

when isMainModule:
  echo horses(15)    #=> 2730
  echo horses(12)    #=> 1320
  echo horses(2)     #=> 2
  echo horses(11)    #=> 990
  # echo horses(a)   #=> compiler error

[Idan Arye]

If the number of horses is 3 or less, return the input value.

Shouldn't that be "less than 3"? Shouldn't horses(3) return 6?

[Rafael Acioly]

Python solution 🐍

from intertools import permutations

WINNERS_QUANTITY = 3


def winner_combination(horses_amount: int) -> int:
    if horses_amount <= WINNERS_QUANTITY:
        return horses_amount

    possibilities = list(permutations(
        range(horses_amount), WINNERS_QUANTITY
    ))
    return len(possibilities)

[Cent]

Good old factorials. I had fun with this one. Feel free to give advice if I can make my code better!

JS

CodePen

Edit: forgot to convert the input to a number making all of the numbers that go through the function a string

// grabs the input, the number of horses, from the input tag
const calculate = (horses = Number(document.querySelector("#horses").value)) => {

  //puts the answer into an empty div
  document.querySelector("#answer").innerHTML = 
    horses !== parseInt(horses) ? undefined :
    horses < 4 ? horses :
    factorial(horses)/factorial(horses - 3);
}

const factorial = (n) => {
  return n ? n * factorial(n - 1) : 1;
}

[Brett Martin]

Shortest answer I could think of:

const horses = n => { 
    if(Number.isInteger(n)) return n < 3 ? n : n * (n-1) * (n-2)
};

And in Standard ML, since it has type checking I can skip the int check:

fun horses(n: int) : int = if n < 3 then n else n * (n - 1) * (n - 2)

[Nick Holmes]

The code (F#)

let WinnerCombinations n =
    if (n <= 3) then None
    else Some (n * (n-1) * (n-2))

As F# is a strongly typed language, no need to check n is an integer - it is. Idiomatically, "undefined" in F# is handled with the Option monad, so we return either None or Some result.

The actual calculation is trivial; n * (n-1) * (n-2)

[SavagePixie]

My JavaScript solution:

const winCombos = n => !Number.isInteger(n)
    ? undefined
    : n < 4
    ? n
    : n * (n - 1) * (n - 2)

[Vaibhav Yadav]

In Go.

func horses(num uint64) uint64 {
    if num <= 3 {
        return num
    }
    return num * (num - 1) * (num - 2)
}