title: Friends Pairing Problem 2
signature: def friendsPairingProblem2(n: Int) = {
test_code: import scala.collection.mutable.HashMap
  import scala.collection.immutable.HashSet
  
  
  // SOLUTION CODE
  // ============================================
  PLACEHOLDER_CODE_BODY
  
  
  // TESTING CODE 
  // ============================================
  def validateSolution(actual: Long , expected: Long): Boolean = {
      actual.toString == expected.toString
  }
  
  def driver(n: Int, expected: Long): String = {
      try {
          if (validateSolution(PLACEHOLDER_FN_NAME(n),expected)) {
              "PASSED"
          } else{
              "FAILED"
          }
      }catch{
          case e: Exception => {e.getClass.getName}
      }
  
  }
  object QuestionEvaluator extends App {
  
      println(s"TEST-0...${driver(
        24, 
        17492190577600L    
      )}")   
  
  
      println(s"TEST-1...${driver(
        1, 
        1L    
      )}")   
  
  
      println(s"TEST-2...${driver(
        29, 
        101990226254706560L    
      )}")   
  
  
      println(s"TEST-3...${driver(
        3, 
        4L    
      )}")   
  
  
      println(s"TEST-4...${driver(
        14, 
        2390480L    
      )}")   
  
  }
  
source_py: def friends_pairing_problem_2(n):
      (a, b, c) = (1, 2, 0)
      if (n <= 2):
          return n
      for i in range(3, (n + 1)):
          c = (b + ((i - 1) * a))
          a = b
          b = c
      return c
source_cpp: int friends_pairing_problem_2(int n) {
    int a = 1, b = 2, c = 0;
    if ( n <= 2 ) {
      return n;
    }
    for ( int i = 3;
    i <= n;
    i ++ ) {
      c = b + ( i - 1 ) * a;
      a = b;
      b = c;
    }
    return c;
  }