old_from_binary.rs

pub fn from_binary(s: &str) -> Option<u32> {
  let total: u32 = s.chars().rev().enumerate().map(|c| {
    let (i, c) = c;

    if c == '1' {
      (2 as u32).pow(i as u32)
    } else {
      0
    }
  }).sum();

  return Some(total);
}