Posted on Oct 10, 2019

Daily Challenge #87 - Pony Express

The Pony Express was a mail service that operated from 1859-60 in the United States. It was made completely obsolete by the intercontinental telegraph.

There were a number of stations where a rider would stop to switch to a fresh horse, or pass the mail bag along to another rider to continue the trek.

stations is an array/list of distances in miles from one station to the next along the route.

Implement a riders function, to return how many riders it would take to get from point A to point B. Riders will never agree to riding more than 100 miles.

example: stations = [43, 23, 40, 13]
output: 2 riders

Good luck!

This challenge comes from dinglemouse on CodeWars. Thank you to CodeWars, who has licensed redistribution of this challenge under the 2-Clause BSD License!

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Top comments (14)

Michael Baas • Oct 10 '19

The question is a bit unclear: it speaks about getting from A to B and then lists 4 points. I assume that A is the first and B the last.
So then...

APL (Dyalog APL)

The complete program:

 riders←{⌈.01×+/⍵}

Testing...

 riders 43 23 40 13 2

Try it online!

K.V.Harish • Oct 10 '19 • Edited

My solution in js

const riders = (stations = []) => { let numOfRiders = + !!stations.reduce((acc, distance) => acc + distance, 0), totalDistance = 0; stations.forEach((distance) => { if(totalDistance + distance <= 100) { totalDistance += distance; } else { numOfRiders++; totalDistance = distance; } }); return numOfRiders; }; console.log(riders()); // 0 console.log(riders([])); // 0 console.log(riders([0, 0, 0, 0, 0])); // 0 console.log(riders([43, 23, 40, 13])); // 2 console.log(riders([100, 100, 100, 50, 50, 30, 20, 25, 25, 25, 25])); // 6

Blessed T Mahuni • Oct 11 '19

Nice your solution is a little bit on an expert level here my JS solution

function riders(stations) { // check if stations is defined if(stations) { let distanceRode = 0 let numberOfRiders = 0 stations.forEach(distance => { distanceRode += distance }); //Check if there is anything passed within the array if(distanceRode == 0) return 0 //modulus division let i = distanceRode%100 //check if distance is greater than 100 if (distanceRode >= 100) { if(i == 0) { /* if distance is greater than 100 and modulus division is 0 then simply divide by 100 to get distance rode */ numberOfRiders = distanceRode/100 } else { /* if distance is greater than 100 and modulus division is not 0 then simply divide by 100 to get number of riders and set the remainder as an extra rider */ numberOfRiders = Math.floor(distanceRode/100) + 1 } } return numberOfRiders } else { return 0 } } console.log(riders()); // 0 console.log(riders([])); // 0 console.log(riders([0, 0, 0, 0, 0])); // 0 console.log(riders([43,23,40,13])) //2 console.log(riders([34,56,12,67,23,90,56])) //4 console.log(riders([56,67,100,345,12,45])) //7 console.log(riders([100, 100, 100, 50, 50, 30, 20, 25, 25, 25, 25])); //6

K.V.Harish • Oct 12 '19

Good approach. Taking the total and dividing by 100 to see how many riders.

ddowy • Feb 4 '22

is the + !!stations just to add one?

SavagePixie • Oct 11 '19

Gotta love that .reduce()

const riders = stations => { const total = stations.reduce((a, b) => a.currentMiles + b <= 100 ? { currentMiles: a.currentMiles + b, riders: a.riders } : { currentMiles: b, riders: a.riders + 1 }, { currentMiles: 0, riders: 1 }) return total.riders }

It could also be done as a one-liner with something like this, but it's a lot less clear:

const riders = s => s.reduce(([a, r], d) => a + d <= 100 ? [a+d, r] : [d, r+1], [0,1])[1]

Avalander • Oct 12 '19

My challenge is writing this is Haskell on the phone without running the code.

calc_riders :: [Int] -> Int calc_riders = fst . foldl count (1, 0) count :: (Int, Int) -> Int -> (Int, Int) count (r, m) x | m + x > 100 = (r + 1, m) | otherwise = (r, m + x)

Amin • Oct 10 '19

Elm

module PonyExpress exposing (riders) riders : List Int -> Int riders stations = ceiling <| toFloat (List.sum stations) / 100

Tests

module PonyExpressTest exposing (suite) import Expect exposing (equal) import PonyExpress exposing (riders) import Test exposing (Test, describe, test) suite : Test suite = describe "Pony express" [ test "It should return 2 for a total ride of 119 miles" <| \_ -> equal 2 <| riders [ 43, 23, 40, 13 ] , test "It should return 1 for a total ride of 100 miles" <| \_ -> equal 1 <| riders [ 43, 23, 34 ] , test "It should return 0 for a total ride of 0 miles" <| \_ -> equal 0 <| riders [ 0 ] ]

Playground

Hosted here on Ellie App.

Jaume Viñas Navas • Oct 11 '19

This is a Swift solution:

func riders(stations: [Int]) -> Int { var n = 1 var d = 0 for distance in stations { if (d + distance > 100) { n += 1 d = distance } else { d += distance } } return n }

Gab • Oct 11 '19

Clojure:

(def stations [43 23 40 13]) (defn riders [lst] "Calculate the number of riders it takes to go to each station" (loop [stations lst rider 1 traveled 0] (cond (empty? stations) rider (> (+ traveled (first stations)) 100) (recur (cons (- (+ traveled (first stations)) 100) (rest stations)) (inc rider) 0) :else (recur (rest stations) rider (+ traveled (first stations)))))) (riders stations) ;; 2

Afief S • Oct 11 '19

In reason:

let countRiders = (stations: list(int)) => { let total = List.fold_right((acc, it) => { acc +. it }, List.map(float, stations), 0.0); int_of_float(ceil(total /. 100.0)) }

Here on sketch: sketch.sh/s/uYFZAhtZSc2Ya4r6t1GNKM/

Gustavo Flores • Oct 11 '19

My code in JS

const riders = (array = []) => Math.ceil(array.reduce((a, b) => a + b, 0) / 100);

Zohar Peled • Oct 11 '19

c#:

int Riders(int[] stations) { var totalSum = stations.Sum(); return (totalSum / 100) + (totalSum % 100 == 0 ? 0 : 1); }

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