title: Tail Recursion
signature: pub fn tail_recursion(n: i32) -> i64 {
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: i64, expected: i64)->bool{
  return actual==expected
  }
  pub fn driver(n: i32, expected: i64)->String{
      if validate_solution(PLACEHOLDER_FN_NAME(n), expected) {
        return "PASSED".to_string();
      };
      return "FAILED".to_string();
  
  }
  
  fn main() {
      println!("TEST-0...{}", driver(
        16, 
        20922789888000
      ));
      
  }
source_py: def tail_recursion(n):
      if (n == 0):
          return 1
      return (n * tail_recursion((n - 1)))
source_cpp: unsigned int tail_recursion(unsigned int n) {
    if ( n == 0 ) return 1;
    return n * tail_recursion ( n - 1 );
  }