title: Count Possible Groups Size 2 3 Sum Multiple 3
signature: countPossibleGroupsSize23SumMultiple3(arr, n) {
test_code: import 'dart:convert';
  
  // SOLUTION CODE
  // ============================================
  PLACEHOLDER_CODE_BODY
  
  // TESTING CODE 
  // ============================================
  bool validateSolution(double actual, double expected){
      return (actual - expected).abs() < 1e-06;
  }
  
  String driver(arr, n, double expected){
      try
      {
          if (validateSolution(PLACEHOLDER_FN_NAME(arr, n), expected)){
              return "PASSED";
          }
          return "FAILED";
      }catch(exception_object){
          return exception_object.runtimeType.toString();
      }
  }
  
  int main() {
  
      print("TEST-0...${driver(
          [1, 3, 6, 12, 18, 31, 36, 43, 47, 59, 64, 64, 69, 69, 94, 98, 98], 12, 
          90.0)
      }");
  
      print("TEST-1...${driver(
          [94, 46, 64, 18, 70, 22, -98, 52, -26, 34, -22, 22, 40, 66, -72, -66, 86, 84, 12, -38, 28, -60, -10, -30, -78, 76, 62, 74, 24, -64, 0, 92, -20, -66, -52], 23, 
          655.0)
      }");
  
      print("TEST-2...${driver(
          [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1], 29, 
          3276.0)
      }");
  
      print("TEST-3...${driver(
          [68, 96, 74, 38, 70, 70], 5, 
          7.0)
      }");
  
      print("TEST-4...${driver(
          [-88, -74, -70, -64, -64, -64, -58, -52, -18, -10, -6, 4, 4, 28, 44, 48, 52, 54, 64, 72, 76, 94], 18, 
          329.0)
      }");
  
      print("TEST-5...${driver(
          [0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 1, 0, 1, 1, 1, 1, 1, 0, 0, 1, 0, 0, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 0, 1, 1, 0, 0, 0, 0, 1, 0, 0, 1], 36, 
          2310.0)
      }");
  
      print("TEST-6...${driver(
          [9, 12, 14, 21, 27, 28, 45, 50, 54, 57, 58, 62, 78, 82, 91, 92, 95], 9, 
          49.0)
      }");
  
      print("TEST-7...${driver(
          [16, -46, -32, -36, -84, -14, -18, 16, 54, 90, -4], 8, 
          24.0)
      }");
  
      print("TEST-8...${driver(
          [0, 0, 1, 1], 3, 
          1.0)
      }");
  
      print("TEST-9...${driver(
          [53, 32, 54, 84, 79, 37, 44, 30, 92, 53, 89, 95], 8, 
          29.0)
      }");
  
      return 0;
  }
source_py: def count_possible_groups_size_2_3_sum_multiple_3(arr, n):
      c = [0, 0, 0]
      res = 0
      for i in range(0, n):
          c[(arr[i] % 3)] += 1
      res += ((c[0] * (c[0] - 1)) >> 1)
      res += (c[1] * c[2])
      res += (((c[0] * (c[0] - 1)) * (c[0] - 2)) / 6)
      res += (((c[1] * (c[1] - 1)) * (c[1] - 2)) / 6)
      res += (((c[2] * (c[2] - 1)) * (c[2] - 2)) / 6)
      res += ((c[0] * c[1]) * c[2])
      return res
source_cpp: int count_possible_groups_size_2_3_sum_multiple_3(vector<int> arr, int n) {
    int c [ 3 ] = {
      0 },
      i;
      int res = 0;
      for ( i = 0;
      i < n;
      i ++ ) c [ arr [ i ] % 3 ] ++;
      res += ( ( c [ 0 ] * ( c [ 0 ] - 1 ) ) >> 1 );
      res += c [ 1 ] * c [ 2 ];
      res += ( c [ 0 ] * ( c [ 0 ] - 1 ) * ( c [ 0 ] - 2 ) ) / 6;
      res += ( c [ 1 ] * ( c [ 1 ] - 1 ) * ( c [ 1 ] - 2 ) ) / 6;
      res += ( ( c [ 2 ] * ( c [ 2 ] - 1 ) * ( c [ 2 ] - 2 ) ) / 6 );
      res += c [ 0 ] * c [ 1 ] * c [ 2 ];
      return res;
    }