Question

This question is about removing sequences from an array, not duplicates in the strict sense.

Consider this sequence of elements in an array;

[0] a [1] a [2] b [3] c [4] c [5] a [6] c [7] d [8] c [9] d 

In this example I want to obtain the following…

[0] a [1] b [2] c [3] a [4] c [5] d 

Notice that duplicate elements are retained but that sequences of the same element have been reduced to a single instance of that element.

Further, notice that when two lines repeat they should be reduced to one set (of two lines).

[0] c [1] d [2] c [3] d 

…reduces to…

[0] c [1] d 

I’m coding in C# but algorithms in any language appreciated.

Answer 1

Here’s C# app i wrote that solves this problem.

takes
aabccacdcd

outputs
abcacd

Probably looks pretty messy, took me a bit to get my head around the dynamic pattern length bit.

class Program {     private static List<string> values;     private const int MAX_PATTERN_LENGTH = 4;      static void Main(string[] args)     {         values = new List<string>();         values.AddRange(new string[] { 'a', 'b', 'c', 'c', 'a', 'c', 'd', 'c', 'd' });           for (int i = MAX_PATTERN_LENGTH; i > 0; i--)         {             RemoveDuplicatesOfLength(i);         }          foreach (string s in values)         {             Console.WriteLine(s);         }     }      private static void RemoveDuplicatesOfLength(int dupeLength)     {         for (int i = 0; i < values.Count; i++)         {             if (i + dupeLength > values.Count)                 break;              if (i + dupeLength + dupeLength > values.Count)                 break;              var patternA = values.GetRange(i, dupeLength);             var patternB = values.GetRange(i + dupeLength, dupeLength);              bool isPattern = ComparePatterns(patternA, patternB);              if (isPattern)             {                 values.RemoveRange(i, dupeLength);             }         }     }      private static bool ComparePatterns(List<string> pattern, List<string> candidate)     {         for (int i = 0; i < pattern.Count; i++)         {             if (pattern[i] != candidate[i])                 return false;         }          return true;     } } 

fixed the initial values to match the questions values