Change Date Format

An application that you are implementing requires multiple date formats to be transformed into one common date format.

Implement the function ChangeDateFormat which accepts a list of strings, representing dates, and returns a new list with each date in the format YYYYMMDD. All incoming dates will be valid dates, but only those in one of the following formats: YYYY/MM/DD, DD/MM/YYYY, and MM-DD-YYYY should be included in the returned list, where YYYY, MM, and DD are numbers representing year, month, and day.

For example, ChangeDateFormat(new List {"2010/03/30","15/12/2016", "11-15-2012", "20130720"}); should return the list {"20100330", "20161215", "20121115"}.

using System;
using System.Collections.Generic;

public class DateTransform
{
public static List< string> ChangeDateFormat(List< string> dates)
{
throw new InvalidOperationException("Waiting to be implemented.");
}

public static void Main(string[] args)
{
var input = new List< string> {"2010/03/30", "15/12/2016", "11-15-2012", "20130720"};
DateTransform.ChangeDateFormat(input).ForEach(Console.WriteLine);
}
}