alternate_string.dart

/// You are given a string containing characters  and  only. Your task is to change it into a string such that there are no matching adjacent characters. To do this, you are allowed to delete zero or more characters in the string.
//
// Your task is to find the minimum number of required deletions.
// https://www.hackerrank.com/challenges/alternating-characters

int alternateCharactersLoop(String input) {
  if (input.isEmpty) {
    return 0;
  }
  var first = input[0];
  var counter = 0;
  for (var i = 1; i < input.length; i++) {
    if (first == input[i]) {
      counter++;
    }
    first = input[i];
  }
  return counter;
}

int alternateCharactersRecursive(String input) {
  if (input.isEmpty) {
    return 0;
  }
  var first = input[0];
  return _inner(input.substring(1), first, 0);
}

int _inner(String input, String char, int counter) {
  if (input.isEmpty) {
    return counter;
  }
  return _inner(
      input.substring(1), input[0], char == input[0] ? ++counter : counter);
}

void main() {
  print("Alternate chars");
  print(alternateCharactersRecursive("aaaaaaabbcaa"));
  print(alternateCharactersRecursive("aabbccc"));
  print(alternateCharactersLoop("aaaaaaabbcaa"));
  print(alternateCharactersLoop("aabbccc"));
}