title: Friends Pairing Problem 2
signature: func friendsPairingProblem2(n int) int64 {
test_code: package main
  
  import (
      "fmt"
      "reflect"
      "math"
      "sort"
  )
  
  // SOLUTION CODE
  // ===================================
  PLACEHOLDER_CODE_BODY
  
  // TESTING CODE
  // ===================================
  func validateSolution(actual int64, expected int64) bool {
      return reflect.DeepEqual(actual,expected)
  }
  
  func driver(n int, expected int64) string {
      if validateSolution(PLACEHOLDER_FN_NAME(n),expected) {
              return "PASSED"
      }
      return "FAILED"
  
  }
  
  func main() {
  
      // Use imports to avoid undefined errors
      var _ = reflect.DeepEqual
      _ = math.Abs
      _ = sort.Sort
      result := ""
      result = driver(24, 17492190577600)
      fmt.Printf("TEST-0...%s\n", result)
      
      result = driver(1, 1)
      fmt.Printf("TEST-1...%s\n", result)
      
      result = driver(29, 101990226254706560)
      fmt.Printf("TEST-2...%s\n", result)
      
      result = driver(3, 4)
      fmt.Printf("TEST-3...%s\n", result)
      
      result = driver(14, 2390480)
      fmt.Printf("TEST-4...%s\n", result)
      
          
  }
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;
  }