title: Hexagonal Number
signature: pub fn hexagonal_number(n: i32) -> i32 {
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: i32, expected: i32)->bool{
  return actual==expected
  }
  pub fn driver(n: i32, expected: i32)->String{
      if validate_solution(PLACEHOLDER_FN_NAME(n), expected) {
        return "PASSED".to_string();
      };
      return "FAILED".to_string();
  
  }
  
  fn main() {
      println!("TEST-0...{}", driver(
        38, 
        2850
      ));
      
      println!("TEST-1...{}", driver(
        44, 
        3828
      ));
      
      println!("TEST-2...{}", driver(
        58, 
        6670
      ));
      
      println!("TEST-3...{}", driver(
        10, 
        190
      ));
      
      println!("TEST-4...{}", driver(
        31, 
        1891
      ));
      
      println!("TEST-5...{}", driver(
        53, 
        5565
      ));
      
      println!("TEST-6...{}", driver(
        94, 
        17578
      ));
      
      println!("TEST-7...{}", driver(
        64, 
        8128
      ));
      
      println!("TEST-8...{}", driver(
        71, 
        10011
      ));
      
      println!("TEST-9...{}", driver(
        59, 
        6903
      ));
      
  }
source_py: def hexagonal_number(n):
      return (n * ((2 * n) - 1))
source_cpp: int hexagonal_number(int n) {
    return n * ( 2 * n - 1 );
  }