title: Count Possible Groups Size 2 3 Sum Multiple 3
signature: pub fn count_possible_groups_size_2_3_sum_multiple_3(arr: Vec<i32>, n: i32) -> f32 {
test_code: use std::collections::HashMap;
  use std::collections::HashSet;
  use std::cmp::*;
  use std::collections::*;
  use std::fmt::*; 
  
  
  // SOLUTION CODE
  // ============================================
  PLACEHOLDER_CODE_BODY
  
  // TESTING CODE 
  // ============================================
  pub fn validate_solution(actual: f32, expected: f32)->bool{
  return (actual - expected).abs() < 1e-06
  }
  pub fn driver(arr: Vec<i32>, n: i32, expected: f32)->String{
      if validate_solution(PLACEHOLDER_FN_NAME(arr, n), expected) {
        return "PASSED".to_string();
      };
      return "FAILED".to_string();
  
  }
  
  fn main() {
      println!("TEST-0...{}", driver(
        Vec::from([1, 3, 6, 12, 18, 31, 36, 43, 47, 59, 64, 64, 69, 69, 94, 98, 98]), 12, 
        90.0
      ));
      
      println!("TEST-1...{}", driver(
        Vec::from([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
      ));
      
      println!("TEST-2...{}", driver(
        Vec::from([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
      ));
      
      println!("TEST-3...{}", driver(
        Vec::from([68, 96, 74, 38, 70, 70]), 5, 
        7.0
      ));
      
      println!("TEST-4...{}", driver(
        Vec::from([-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
      ));
      
      println!("TEST-5...{}", driver(
        Vec::from([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
      ));
      
      println!("TEST-6...{}", driver(
        Vec::from([9, 12, 14, 21, 27, 28, 45, 50, 54, 57, 58, 62, 78, 82, 91, 92, 95]), 9, 
        49.0
      ));
      
      println!("TEST-7...{}", driver(
        Vec::from([16, -46, -32, -36, -84, -14, -18, 16, 54, 90, -4]), 8, 
        24.0
      ));
      
      println!("TEST-8...{}", driver(
        Vec::from([0, 0, 1, 1]), 3, 
        1.0
      ));
      
      println!("TEST-9...{}", driver(
        Vec::from([53, 32, 54, 84, 79, 37, 44, 30, 92, 53, 89, 95]), 8, 
        29.0
      ));
      
  }
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;
    }