struct Solution;
impl Solution {
fn count_primes(n: i32) -> i32 {
if n <= 2 {
return 0;
}
let n: usize = n as usize;
let mut a: Vec<bool> = vec![true; n];
a[0] = false;
a[1] = false;
let mut i: usize = 2;
while i * i < n {
if a[i] {
let mut j = 2;
while j * i < n {
a[i * j] = false;
j += 1;
}
}
i += 1;
}
let sum: i32 = a.iter().fold(0, |sum, &b| if b { sum + 1 } else { sum });
sum
}
}
#[test]
fn test() {
assert_eq!(Solution::count_primes(10), 4);
}