How to check repeated letters in a string c#

Question

I am creating a program that checks repeated letters in a string.

For Example:

wooooooooooow
happpppppppy

This is my code:

 string repeatedWord = "woooooooow";
 for (int i = 0; i < repeatedWord.Count(); i++)
 {
     if (repeatedWord[i] == repeatedWord[i+1])
     {
          // ....
     }
 }

The code works but it will always have an error because the last character [i + 1] is empty/null.

The error is Index was outside the bounds of the array.

Any solution for this?

Solution 1

run the loop until repeatedWord.Count()-1

Solution 2

Regular Expression:

Regex rxContainsMultipleChars = new Regex( @"(?<char>.)\k<char>" , RegexOptions.ExplicitCapture|RegexOptions.Singleline ) ;
.
.
.
string myString = SomeStringValue() ;
bool containsDuplicates = rxDupes.Match(myString) ;

or Linq

string s = SomeStringValue() ;
bool containsDuplicates = s.Where( (c,i) => i > 0 && c == s[i-1] )
                           .Cast<char?>()
                           .FirstOrDefault() != null
                           ;

or roll yer own:

public bool ContainsDuplicateChars( string s )
{
  if ( string.IsNullOrEmpty(s) ) return false ;

  bool containsDupes = false ;
  for ( int i = 1 ; i < s.Length && !containsDupes ; ++i )
  {
    containsDupes = s[i] == s[i-1] ;
  }

  return containsDupes ;
}

Or even

public static class EnumerableHelpers
{
  public static IEnumerable<Tuple<char,int>> RunLengthEncoder( this IEnumerable<char> list )
  {
    char? prev  = null ;
    int   count = 0 ;

    foreach ( char curr in list )
    {
      if      ( prev == null ) { ++count ; prev = curr ; }
      else if ( prev == curr ) { ++count ;               }
      else if ( curr != prev )
      {
        yield return new Tuple<char, int>((char)prev,count) ;
        prev = curr ;
        count = 1 ;
      }
    }
  }
}

With this last one...

bool hasDupes = s.RunLengthEncoder().FirstOrDefault( x => x.Item2 > 1 ) != null ;

or

foreach (Tuple<char,int> run in myString.RunLengthEncoder() )
{
  if ( run.Item2 > 1 )
  {
     // do something with the run of repeated chars.
  }
}

Solution 3

Another option would be using a Regex that matches repeating characters. Then, for each match, you can obtain the number of characters by using the Length property.

string input = "wooooooow happppppppy";
var matches = Regex.Matches(input, @"(.)\1+");
for (int i = 0; i < matches.Count; i++)
{
    Console.WriteLine("\"" + matches[i].Value + "\" is " + matches[i].Length + " characters long.");
    //...
}
Console.Read();

Solution 4

Just "remember" the last letter i would say.

string repeatedWord = "woooooooow";
if (string.IsNullOrEmpty( repeatedWord))
    // empty. return, throw whatever.

char previousLetter = repeatedWord[0]; 
for (int i = 1; i < repeatedWord.Count(); i++)
{
    if (repeatedWord[i] == previousLetter)
    {
        // ....              
    }
    else
    previousLetter = repeatedWord[i];
}

Solution 5

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Delegate
{
    class Program
    {
       public int repeatcount(string str,char ch)
        {

            var count = 0;
            for (int i = 0; i<str.Length; i++)
            {
                if (ch == str[i])
                {
                    count++;
                }

            }

            return count;
        }
        static void Main(string[] args)
        {
            Console.WriteLine("Enter a string");
            string str = Console.ReadLine();
            Console.WriteLine("Enter to know the reperted char");
            char ch = Convert.ToChar(Console.ReadLine());
            Program obj = new Program();
            int p=obj.repeatcount(str, ch);
            Console.WriteLine(p);


            Console.ReadLine();

        }
    }



}

View more solutions

Comments

[Jeroen van Langen]

You'll miss the last letter?

[Pierre-Luc Pineault]

@JeroenvanLangen And you want to check the last letter against what exactly? It will always be different than 'end of line'.

[dav_i]

@JeroenvanLangen new[] { 0, 1, 2 }.Count() == 3

[Jeroen van Langen]

True, true, the last letter = [i+1] missed that... ;) i'd rather avoid index+1 in code. will be less readable and forces programmers to use things like count-1 etc. So could cause more "strange" behaviour

[Michael]

@I4V You're right. This isn't constrained to sequential repeats.

[Servy]

You need to start at the second char if you do this, otherwise you'll fail for looking to the char just before the first.

[Servy]

If you do want to solve this problem, rather than the OP's problem, you'll want to use GroupBy and Count. This solution iterates the sequence many times; it's pretty horrible performance wise.

[Nicholas Carey]

As @Servy said. This, s.GroupBy( c => c ).FirstOrDefault( group => group.Count() > 1 ) != null ; (or something similar) will accomplish the same thing with a lot less work. Your code will run in approximately O(n*^2) time, I believe. O(*mn) actually, with m being the count of distinct characters in the source and n the total number of characters in the source.

[Michael]

@NicholasCarey & Servy - agreed.

[Lakshay Dulani]

hello timothy! can you please explain how does the code do it

[Ramu Vemula]

In the count, we can get the repeated characters value

[Mostafiz]

better you explain more detail