Problem of the Day

Wednesday, November 4, 2026

Problem:

Consider the following method, which is intended to count the number of double-letter occurrences in a string.

/**
 * returns the number of double-letter occurrences in a string
 * Examples: "Ramadan" returns 0, repeated letters aren't sequential
 *           "Christmas" return 0
 *           "Hannukah" return 1 for the double "n"
 *           "Halloween" returns 2 for the doubled "l" and doubled "e"
 */
public static int doubleLetterCounter(String str)
{
    
    /* missing code */
    
}

Which of the following could be used to replace /* missing code */ so that the method will work as intended?

1. 
   

   int count = 0;
   for (int i = 0; i < str.length(); i++)
   {
       if (str.substring(i - 1, i).equals(str.substring(i, i + 1)))
           count++;
   }
   return count;

2. 
   

   int count = 0;
   for (int i = 0; i < str.length(); i++)
   {
       if (str.substring(i, i + 1).equals(str.substring(i + 1, i + 2)))
           count++;
   }
   return count;

3. 
   

   int count = 0;
   for (int i = 1; i < str.length(); i++)
   {
       if (str.substring(i - 1, i).equals(str.substring(i, i + 1)))
           count++;
   }
   return count;

4. 
   

   int count = 0;
   for (int i = 1; i < str.length() - 1; i++)
   {
       if (str.substring(i - 1, i).equals(str.substring(i, i + 1)))
           count++;
   }
   return count;

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