质数检测

  1. pub fn prime_check(num: usize) -> bool {
  2.     if (num > 1) & (num < 4) {
  3.         return true;
  4.     } else if (num < 2) || (num % 2 == 0) {
  5.         return false;
  6.     }
  8.     let stop: usize = (num as f64).sqrt() as usize + 1;
  9.     for i in (3..stop).step_by(2) {
  10.         if num % i == 0 {
  11.             return false;
  12.         }
  13.     }
  14.     true
  15. }
  17. #[cfg(test)]
  18. mod tests {
  19.     use super::*;
  21.     #[test]
  22.     fn basic() {
  23.         assert_eq!(prime_check(3), true);
  24.         assert_eq!(prime_check(7), true);
  25.         assert_eq!(prime_check(11), true);
  26.         assert_eq!(prime_check(2003), true);
  28.         assert_eq!(prime_check(4), false);
  29.         assert_eq!(prime_check(6), false);
  30.         assert_eq!(prime_check(21), false);
  31.         assert_eq!(prime_check(2004), false);
  32.     }
  33. }