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  1. use std::io::{self, BufRead};
  2.  
  3. fn main() {
  4.     let stdin = io::stdin();
  5.     for line in stdin.lock().lines() {
  6.         if line.is_ok() {
  7.             let content = line.unwrap();
  8.             let n: u32 = content.parse().unwrap();
  9.             match reverse_factorial(n) {
  10.                 Some(rev) => {
  11.                     println!("{} = {}!", n, rev);
  12.                 },
  13.                 None => {
  14.                     println!("{} NONE", n);
  15.                 }
  16.             }
  17.         }
  18.     }
  19. }
  20.  
  21. fn reverse_factorial(n: u32) -> Option<u32> {
  22.     let mut num = n;
  23.     let mut div = 2;
  24.  
  25.     while num % div == 0 {
  26.         num /= div;
  27.         div += 1;
  28.     }
  29.  
  30.     if div % num == 0 {
  31.         Some(div - 1)
  32.     } else {
  33.         None
  34.     }
  35. }
  36.  
  37. #[cfg(test)]
  38. mod tests {
  39.     use super::reverse_factorial;
  40.  
  41.     #[test]
  42.     fn it_generates_some_reverse_factorial() {
  43.         let result = reverse_factorial(120);
  44.         println!("{:?}", result);
  45.  
  46.         assert!(result.is_some());
  47.         assert_eq!(5, result.unwrap());
  48.  
  49.         assert_eq!(10, reverse_factorial(3628800).unwrap());
  50.         assert_eq!(12, reverse_factorial(479001600).unwrap());
  51.         assert_eq!(3, reverse_factorial(6).unwrap());
  52.     }
  53.  
  54.     #[test]
  55.     fn it_generates_none_reverse_factorial() {
  56.         let result = reverse_factorial(150);
  57.         println!("{:?}", result);
  58.  
  59.         assert!(result.is_none());
  60.  
  61.         assert!(reverse_factorial(18).is_none());
  62.     }
  63. }
Success #stdin #stdout 0s 12000KB
comments (?)
stdin
copy 
120
150
3628800
479001600
6
18
stdout
copy 
120 = 5!
150 NONE
3628800 = 10!
479001600 = 12!
6 = 3!
18 NONE
https://ideone.com/gcbnRv
language:
Rust (rust 1.56)
created:
7 years ago
visibility:
public

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