09-tortoise-racing.js

/* 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 speed is 850 feet per hour. How long will it take B to catch A?
   More generally: given two speeds v1 (A speed, integer > 0) and v2
   (B speed, integer > 0) and a lead g (integer > 0) how long will it take B to catch A?
   The result will be an array [h, mn, s] where h, mn, s is the time needed in hours,
   minutes and seconds (don't worry for fractions of second).
   If v1 >= v2 then return nil, nothing, null, None or {-1, -1, -1} for C++, C, Go.
   Examples:
   race(720, 850, 70) => [0, 32, 18]
   race(80, 91, 37) => [3, 21, 49]
   Note: you can see some other examples in "Your test cases". */

// solution
export default (v1, v2, g) => {
  const r = g / (v2 - v1);
  return v2 > v1 ? [Math.floor(r), Math.floor((r * 60) % 60), Math.floor((r * 3600) % 60)] : null;
};