find_pairs.dart

/// https://www.hackerrank.com/challenges/pairs/problem

int findPairs(List<int> pairs, int diff) {
  var counter = 0;
  // save all values into Set
  Set map = {};
  for (var el in pairs) {
    map.add(el);
    // use math to determine if there is a value as difference between value and diff
    if (map.contains(el - diff)) {
      counter++;
    }

    // use math to determine if there is a value of sum of element and diff
    if (map.contains(el + diff)) {
      counter++;
    }
  }

  return counter;
}

void main() {
  var input = [1, 2, 3, 4];
  var diff = 1;
  print("Find pairs in array");
  print(findPairs(input, diff));

  input = [1, 5, 4, 2];
  diff = 2;
  print(findPairs(input, diff));
  input = [1, 5, 3, 4, 2];
  diff = 2;
  print(findPairs(input, diff));
  input = [1, 3, 5, 8, 6, 4, 2];
  diff = 2;
  print(findPairs(input, diff));
}