Puzzle: Tortoise racing [reference]

Tortoise racing” is a coding puzzle that people can be attempted in the following languages: ruby, python, javascript, haskell, java, csharp, clojure, coffeescript, cpp, php, crystal, fsharp, c, typescript, rust, swift, go, r, nim, shell, ocaml, kotlin, groovy, fortran, elixir, julia, scala, powershell, reason, and racket.

  • Difficulty: 6 kyu
  • Stars: 877
  • Votes: 1044
  • Category: reference
  • Tags: Fundamentals
  • Source: codewars


Two tortoises named A and B must run a race. A starts with an average speed of

720 feet per hour

Young B knows she runs faster than A, and furthermore has not finished her cabbage.

When she starts, at last, she can see that A has a 70 feet lead but B’s speed is 850 feet per hour.
How long will it take B to catch A?

More generally:
given two speeds v1 (A’s speed, integer > 0) and v2 (B’s speed, integer > 0) and a lead g (integer > 0)
how long will it take B to catch A?

The result will be an array

[hour, min, sec]

which is the time needed in hours, minutes and seconds (round down to the nearest second)
or a string in some languages.

If v1 >= v2 then return nil, nothing, null, None or {-1, -1, -1} for C++, C, Go, Nim, [] for Kotlin or “-1 -1 -1”.


(form of the result depends on the language)

race(720, 850, 70) => [0, 32, 18] or "0 32 18"
race(80, 91, 37)   => [3, 21, 49] or "3 21 49"

** Note:

  • See other examples in “Your test cases”.

  • In Fortran - as in any other language - the returned string is not permitted to contain any redundant trailing whitespace: you can use dynamically allocated character strings.

** Hints for people who don’t know how to convert to hours, minutes, seconds:

  • Tortoises don’t care about fractions of seconds

  • Think of calculation by hand using only integers (in your code use or simulate integer division)

  • or Google: “convert decimal time to hours minutes seconds”

Solve It Here

Click the link below to solve it on Codewars:


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