indexMapping<T> function

Map<T, List<int>> indexMapping<T>(List<T> list)

Maps each element in a list to a list of indices where it appears.

This function returns a map from each unique element in list to a list of all indices where it occurs.

Time Complexity: O(n), where n is the length of the list.

Example:

var result = indexMapping(['a', 'b', 'a', 'c']);
print(result); // Outputs: {'a': [0, 2], 'b': [1], 'c': [3]}

Implementation

Map<T, List<int>> indexMapping<T>(List<T> list) {
  final map = <T, List<int>>{};
  for (var i = 0; i < list.length; i++) {
    map.putIfAbsent(list[i], () => []).add(i);
  }
  return map;
}