/* Java application that includes solutions to the problems in Quiz #2 
** and whose main() method "exercises" those solutions on test data.
**
** Given was the specification of the posOfKth() method, with the
** instruction that it should be used.  The task was to supply the
** bodies of the replace() and remove() methods.
**
** Programming Assignment #4 involved developing Java methods in a
** CSV_Utility class.  Among these was setIthField(), which differs
** from replace() only in technical details.  
*/
public class Quiz2_F25_Sol {

   public static void main(String[] args) {
      String s = "$The$cat$in$the$hat$ate$a$rat$";
      String t = "GLORP";
      for (int k=1; k != 10; k++) {
         System.out.printf("s: \"%s\"; k: %d; t: \"%s\"\n", s, k, t);
         System.out.printf("replace(s,k,t) yields \"%s\"\n", replace(s,k,t));
         System.out.printf("remove(s,k) yields \"%s\"\n\n", remove(s,k));
      }
     
   }

   /* Returns the position, within string s, of the k-th occurrence of ch.
   ** If there are fewer than k occurrences of ch within s, the value returned
   ** is s.length().
   ** pre: k >= 1  &&  s != null
   */
   public static int posOfKth(String s, char ch, int k) { 
      int result;
      int j = 0;
      int count = 0;
      while (j != s.length()  &&  count != k) {
         if (s.charAt(j) == ch) { count = count + 1; }
         j = j+1;
      }
      // assert: if count != k, then j == s.length() and there are
      //         fewer than k occurrences of ch within s.  Otherwise,
      //         the k-th occurrence of ch is at position j-1.
      if (count == k) { j = j-1; }
      return j;
   }


   /* Returns the string resulting from replacing, by String t, the substring
   ** of s in between its k-th and (k+1)-st occurrences of '$'.  If there are
   ** k or fewer occurrences of '$' within s, the string returned is s.
   ** pre: k >= 1  &&  s != null
   */
   public static String replace(String s, int k, String t) { 

      if (posOfKth(s, '$', k+1) == s.length()) {
         // s has k or fewer occurrences of '$', so return s 
         return s;
      }
      else {
         // Find the positions within s of the k-th and (k+1)-st
         // occurrences of '$'.
         int posK = posOfKth(s, '$', k);
         int posKPlus1 = posOfKth(s, '$', k+1);

         // Obtain the prefix of s up to and including the k-th 
         // occurrence of '$', and the suffix of s starting at the
         // (k+1)-st occurrence of '$'.
         String prefix = s.substring(0, posK + 1);
         String suffix = s.substring(posKPlus1);

         // Paste s back together again, but with t replacing the
         // substring in between the k-th and (k+1)-st occurrences of '$'.
         return prefix + t + suffix;
      }
   }



   /* Returns the string resulting from removing from s the characters 
   ** in between its the k-th and (k+1)-st occurrences of '$'.  If there
   ** are k or fewer occurrences of '$' within s, the string returned is s.
   ** pre: k >= 1  &&  s != null
   */
   public static String remove(String s, int k) { 
      // Observe that removing a substring is the same as replacing
      // that substring by the empty string.
      return replace(s, k, ""); 
   }

}