leastOccurrences method

Implementation

(int, int)? leastOccurrences() {
  // check if the list is empty before calling reduce
  if (isEmpty) {
    return null;
  }

  // Create a new HashMap to store each integer and its frequency.
  final HashMap<int, int> frequencyMap = HashMap<int, int>();
  // Iterate over each integer in the list.
  for (final int item in this) {
    // Update the frequency of the current integer in the map, or
    // set it to 1 if it's not in the map yet.
    // ignore: require_future_error_handling
    frequencyMap.update(item, (int value) => value + 1, ifAbsent: () => 1);
  }

  // Find the key-value pair with the lowest value (frequency) in the map.
  // The map is guaranteed non-empty since we checked isEmpty above.
  MapEntry<int, int>? leastCommonEntry;
  for (final MapEntry<int, int> entry in frequencyMap.entries) {
    if (leastCommonEntry == null || entry.value < leastCommonEntry.value) {
      leastCommonEntry = entry;
    }
  }

  // Return a tuple with the least common value and its frequency.
  // leastCommonEntry is guaranteed non-null since the list is non-empty.
  return leastCommonEntry == null ? null : (leastCommonEntry.key, leastCommonEntry.value);
}