title: Count Possible Groups Size 2 3 Sum Multiple 3
signature: class Solution {
  
      public float CountPossibleGroupsSize23SumMultiple3(List<int> arr, int n) {
test_code: using System;
  using System.Numerics;
  using System.Diagnostics;
  using System.Collections.Generic;
  using System.Linq;
  using System.Text;
  using System.Security.Cryptography;
  using System.Web.UI;
  using System.Web.Script.Serialization;
  
  // SOLUTION CODE
  // ============================================
  PLACEHOLDER_CODE_BODY
  
  // TESTING CODE 
  // ============================================
  namespace EvaluatePrediction {
      class TestRunner {
          public bool ValidateSolution(float actual, float expected){
              return Math.Abs(actual - expected) < 1e-06f;
          }
  
          public string driver(List<int> arr, int n, float expected){
              try{
                PLACEHOLDER_CLS_NAME solution_cls = new PLACEHOLDER_CLS_NAME();
                float pred_result = solution_cls.PLACEHOLDER_FN_NAME(arr, n); 
                if (ValidateSolution(
                      pred_result,
                      expected)){
                  return "PASSED";
                }
                return "FAILED";
              } 
              catch (Exception exception_obj)
              {
                return exception_obj.GetType().FullName;
              }
          }
          static void Main(string[] args) {
              TestRunner runner = new TestRunner();
              String result;
              result = runner.driver(
                  new List<int>{1, 3, 6, 12, 18, 31, 36, 43, 47, 59, 64, 64, 69, 69, 94, 98, 98}, 12, 
                  90.0f
              );
              Console.WriteLine(string.Format(
                  "TEST-0...{0}",
                  result)
              );result = runner.driver(
                  new List<int>{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, 
                  655.0f
              );
              Console.WriteLine(string.Format(
                  "TEST-1...{0}",
                  result)
              );result = runner.driver(
                  new List<int>{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, 
                  3276.0f
              );
              Console.WriteLine(string.Format(
                  "TEST-2...{0}",
                  result)
              );result = runner.driver(
                  new List<int>{68, 96, 74, 38, 70, 70}, 5, 
                  7.0f
              );
              Console.WriteLine(string.Format(
                  "TEST-3...{0}",
                  result)
              );result = runner.driver(
                  new List<int>{-88, -74, -70, -64, -64, -64, -58, -52, -18, -10, -6, 4, 4, 28, 44, 48, 52, 54, 64, 72, 76, 94}, 18, 
                  329.0f
              );
              Console.WriteLine(string.Format(
                  "TEST-4...{0}",
                  result)
              );result = runner.driver(
                  new List<int>{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, 
                  2310.0f
              );
              Console.WriteLine(string.Format(
                  "TEST-5...{0}",
                  result)
              );result = runner.driver(
                  new List<int>{9, 12, 14, 21, 27, 28, 45, 50, 54, 57, 58, 62, 78, 82, 91, 92, 95}, 9, 
                  49.0f
              );
              Console.WriteLine(string.Format(
                  "TEST-6...{0}",
                  result)
              );result = runner.driver(
                  new List<int>{16, -46, -32, -36, -84, -14, -18, 16, 54, 90, -4}, 8, 
                  24.0f
              );
              Console.WriteLine(string.Format(
                  "TEST-7...{0}",
                  result)
              );result = runner.driver(
                  new List<int>{0, 0, 1, 1}, 3, 
                  1.0f
              );
              Console.WriteLine(string.Format(
                  "TEST-8...{0}",
                  result)
              );result = runner.driver(
                  new List<int>{53, 32, 54, 84, 79, 37, 44, 30, 92, 53, 89, 95}, 8, 
                  29.0f
              );
              Console.WriteLine(string.Format(
                  "TEST-9...{0}",
                  result)
              );
          }
      }
  }
  
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;
    }