fn main() {
    println!("Hello, world!");
    let tests = [
        ("a1c1e1", "abcdef"),
        ("a1b2c3d4e", "abbdcfdhe")
    ];
    for (input, output) in tests {
        let result = Solution::replace_digits(input.to_string());
        println!("{input:?} is {result:?} should be {output:?}");
    }
}

struct Solution;

impl Solution {
    pub fn replace_digits(mut s: String) -> String {
        unsafe {s.as_bytes_mut()}.chunks_exact_mut(2).for_each(|x| x[1] = x[0] + x[1] - b'0');
        s
    }
}