Codefights

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Curious Clock

Description

Benjamin recently bought a digital clock at a magic trick shop. The seller never told Ben what was so special about it, but mentioned that one day Benjamin would be faced with a surprise.

Indeed, the clock did surprise Benjamin: without warning, at someTime the clock suddenly started going in the opposite direction! Unfortunately, Benjamin has an important meeting very soon, and knows that at leavingTime he should leave the house so as to not be late. Ben spent all his money on the clock, so has to figure out what time his clock will show when it’s time to leave.

Given the someTime at which the clock started to go backwards, find out what time will be shown on the curious clock at leavingTime.

For your convenience, here is the list of months lengths (from January to December, respectively):

Months lengths: 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31. Please, note that in leap years February has 29 days.

Note (leap years): Year is leap if its number is divisible by 4 and isn’t divisible by 100 or if its number is divisible by 400.

Example

For someTime = "2016-08-26 22:40" and leavingTime = "2016-08-29 10:00", the output should be curiousClock(someTime, leavingTime) = "2016-08-24 11:20".

There are 2 days, 11 hours and 20 minutes till the meeting. Thus, the clock will show 2016-08-24 11:20 at the leavingTime.

Input/Output

  • [execution time limit] 4 seconds (js)

  • [input] string someTime

    The time at which the clock started going backwards. It is guaranteed that the time is correct.
    The time is given in the format "YYYY-MM-DD HH:MM".

    Guaranteed constraints:
    1970-01-01 00:00 ≤ someTime.

  • [input] string leavingTime

    The time at which Ben will have to leave for the meeting in the same format as someTime and with the same constraints.

    Guaranteed constraints:
    someTime < leavingTime,
    leavingTime ≤ 2035-12-31 23:59.

  • [output] string

    • The time Ben’s curious clock will show when it’s time to leave in the same format as leavingTime and someTime. It is guaranteed that it will be not earlier than the midnight of January the 1st, 1970.

[JavaScript (ES6)] Syntax Tips

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// Prints help message to the console
// Returns a string
function helloWorld(name) {
console.log("This prints to the console when you Run Tests");
return "Hello, " + name;
}

Solution

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function curiousClock(someTime, leavingTime) {
  var date = new Date();
  date.setTime(2 * Date.parse(someTime) - Date.parse(leavingTime));
  var year = date.getFullYear();
  var month = "0" + (date.getMonth() + 1);
  var day = "0" + date.getDate();
  var hours = "0" + date.getHours();
  var minutes = "0" + date.getMinutes();
  return `${year}-${month.substr(-2)}-${day.substr(-2)} ${hours.substr(
    -2
  )}:${minutes.substr(-2)}`;
}