Time Math Interview Problem (C# Solution)

This is a solution for the problem posted by Ali Abbas Rizvi here. Command line arguments are method name (e.g. AddMinutes), start time (e.g. 9:24AM), and minutes to add (e.g. 18). The result will be the new time after addminutes in the same time format.

using System;
using System.Text.RegularExpressions;
using System.Collections.Specialized;

namespace SolvingSmallProblems
{
class Program
{
static void Main(string[] args)
{
TimeConversions timeConv = new TimeConversions();

string commandName;
string baseTime;
string incrementalTime;
string output;
if (args.GetLength(0) == 3)
{
commandName = args[0];
baseTime = args[1];
incrementalTime = args[2];

switch (commandName.ToUpper())
{

case (“ADDMINUTES”):
output = timeConv.AddMinutes(baseTime, Int32.Parse(incrementalTime));
Console.Out.WriteLine(output);
Console.Out.Flush();
break;
}
}
else
{
throw new Exception(“Incorrect number of arguments: 2 expected…”);
}

}

}

class TimeConversions
{
private StringCollection meridiemValidValues;
public StringCollection methodsAvailable;

public TimeConversions()
{
meridiemValidValues = new StringCollection();
meridiemValidValues.Add(“AM”);
meridiemValidValues.Add(“PM”);

methodsAvailable = new StringCollection();
methodsAvailable.Add(“AddMinutes”);
}

public string AddMinutes(string time, int minutesToAdd)
{
long convertedTime = ConvertTimeToMinutes(time);
string finalTime = ConvertMinutesToTime(convertedTime + minutesToAdd);
return finalTime;
}

private string ConvertMinutesToTime(long minutes)
{
long calculatingHours;
long calculatingMinutes;
string calculatingMeridiem;

calculatingMinutes = minutes % 60;
// Rolling over hours for a 24-hour clock
calculatingHours = (minutes / 60) % 24;

if (calculatingHours < 12) { calculatingMeridiem = "AM"; // 0 am should be written as 12 am if (calculatingHours == 0) { calculatingHours = 12; } } else { calculatingMeridiem = "PM"; calculatingHours -= 12; } return calculatingHours.ToString() + ":" + calculatingMinutes.ToString().PadLeft(2, '0') + " " + calculatingMeridiem; } private long ConvertTimeToMinutes(string time) { long normalizedTime; string regexStringForTimeConversion = @"^(?[\d]{1,2}):(?\d\d)[\s]?(?[AP]M)$”;
Regex regexForTimeConversion = new Regex(regexStringForTimeConversion);

Match matchedTime = regexForTimeConversion.Match(time);
int hours, minutes;
string meridiem;
try
{
hours = Int32.Parse(matchedTime.Groups[“Hours”].Value);
}
catch (Exception)
{
throw new Exception(“Invalid characters in Hours!”);
}
try
{
minutes = Int32.Parse(matchedTime.Groups[“Minutes”].Value);
}
catch (Exception)
{
throw new Exception(“Invalid characters in Minutes!”);
}
if (meridiemValidValues.Contains( matchedTime.Groups[“Meridiem”].Value))
{
meridiem = matchedTime.Groups[“Meridiem”].Value;
}
else
{
throw new Exception(“Invalid characters in Meridiem!”);
}

// Rule: 12 PM will be 12 in a 24-hour clock, 12 AM will be 0
if ((hours == 12) && (meridiem == “AM”))
{
hours = 0;
}
else if ((hours < 12) && (meridiem == "PM")) { hours += 12; } normalizedTime = (hours * 60) + minutes; return normalizedTime; } } } [/sourcecode]