expand_simplify.dart

// ignore_for_file: avoid_print

// Input: [[1, 2], [3, 4]]
// Desired output: [3,1, 3,2, 4,1, 4,2]

void main() {
  List<List<int>> nestedArray = [
    [1, 2],
    [3, 4],
    [5],
  ];

  print("\nINPUT: $nestedArray");

  // #1. Convert from nested array to map
  Map nestedMap = nestedArrToMap(nestedArray);
  print("\n#1 CONVERTED TO MAP:");
  print(nestedMap);

  // #2. Extract nested key from map which is expected result
  List<String> keys = getNestedKeys(nestedMap);
  print("\n#2 MAP TO KEYS:");
  print(keys);

  print("\nRESULT IN LIST:");
  print(keys.map((e) => e.split(",")));

  print("");
}

/// Input: [[1, 2], [3, 4]]
/// Output:
/// {
///  3: {
///    1: {},
///    2: {}
///  },
///  4: {
///    1: {},
///    2: {}
///  }
/// }
Map nestedArrToMap(List<List<int>> nestedArray) {
  Map nestedMap = {};
  int? currentStart;

  for (int i = 0; i < nestedArray.length; i++) {
    List<int> array = nestedArray[i];
    for (int j = 0; j < array.length; j++) {
      String element = nestedArray[i][j].toString();
      if (currentStart == i) {
        nestedMap[element] = {...nestedMap}.values.first;
      } else {
        currentStart = i;
        
        // set previous map to new map of one element        
        Map tmpNestedMap = {};
        tmpNestedMap[element] = {...nestedMap};
        nestedMap = tmpNestedMap;        
      }
    }
  }

  return nestedMap;
}

// Reference: https://stackoverflow.com/a/56930729/13989964
//
/// Input:
/// {
///  3: {
///    1: {},
///    2: {}
///  },
///  4: {
///    1: {},
///    2: {}
///  }
/// }
///
/// Output: [3,1, 3,2, 4,1, 4,2]
List<String> getNestedKeys(dynamic object, [String? prevKey, List<String> keys = const []]) {
  if (object is Map && object.isNotEmpty) {
    List<String> newKeys = [];

    object.forEach((key, value) {
      String newKey = key;
      if (prevKey != null) newKey = "$prevKey,$key";
      final privatedKeys = getNestedKeys(value, newKey, []);
      newKeys.addAll(privatedKeys);
    });

    return newKeys;
  } else {
    if (prevKey != null) keys.add(prevKey);
    return keys;
  }
}

OUTPUT:

INPUT: [[1, 2], [3, 4], [5]]

#1 CONVERTED TO MAP:
{5: {3: {1: {}, 2: {}}, 4: {1: {}, 2: {}}}}

#2 MAP TO KEYS:
[5,3,1, 5,3,2, 5,4,1, 5,4,2]

RESULT IN LIST:
([5, 3, 1], [5, 3, 2], [5, 4, 1], [5, 4, 2])