reordered_powers.rs

use std::iter::successors;

lazy_static! {
    static ref POWS: Vec<u64> = (0..30).map(|x| 1 << x).map(digit_map).collect();
}
      
impl Solution {
  pub fn reordered_power_of2(n: i32) -> bool {
      POWS.contains(&digit_map(n))
  }
}

fn digit_map(n: i32) -> u64 {
    successors(Some(n), |&x| Some(x / 10))
        .take_while(|&x| x > 0)
        .map(|x| x % 10)
        .fold(0, |m, c| {
            let mask = 0b1111 << 4 * c;
            let count = ((m & mask) >> 4 * c) + 1;
            m & (!0 ^ mask) | (count << 4 * c)
        })
}