twoSum<T> function

List<int>? twoSum<T>(List<T> nums, T target)

Finds two indices in the list nums whose elements sum up to target.

This function works with generic type T where == and subtraction are supported. However, Dart currently does not support operator constraints on generics, so this implementation assumes T is int or a similar numeric type.

Returns a list containing the two indices if such a pair exists, otherwise returns null.

Example:

var result = twoSum<int>([2, 7, 11, 15], 9);
print(result); // Outputs: [0, 1]

Implementation

List<int>? twoSum<T>(List<T> nums, T target) {
  final Map<T, int> numToIndex = {};

  for (int i = 0; i < nums.length; i++) {
    T current = nums[i];

    // Dart doesn't support arithmetic operators in generics directly,
    // so to make this generic, you'd need additional mechanisms or restrict to int.
    // For now, we cast to dynamic and rely on runtime.
    dynamic complement = (target as dynamic) - (current as dynamic);

    if (numToIndex.containsKey(complement)) {
      return [numToIndex[complement]!, i];
    }

    numToIndex[current] = i;
  }

  return null;
}