Suuremmat

warning: variable does not need to be mutable
 --> input/code.rs:7:9
  |
7 |     let mut chars = chars.map(|(_, x)| x);
  |         ----^^^^^
  |         |
  |         help: remove this `mut`
  |
  = note: `#[warn(unused_mut)]` on by default

use std::io::{self, BufRead};

fn suurempi(s: &str) {
    let mut chars = s.chars().enumerate().skip_while(|&(_, x)| x == '0');
    let (size, first) = chars.next().unwrap();
    let size = s.len() - size;
    let mut chars = chars.map(|(_, x)| x);
    let mut exact = true;
    for c in chars {
        match c {
            '0'..='9' => {
                if c as u8 > first as u8 {
                    println!("{}", [((first as u8 + 1) as char)].iter().cycle().take(size).collect::<String>());
                    return;
                } else if (c as u8) < first as u8 {
                    exact = false;
                }
            }
            '\n' => {
                break;
            }
            _ => panic!(),
        }
    }
    if exact && first != '9' {
        println!("{}", [((first as u8 + 1) as char)].iter().cycle().take(size).collect::<String>());
    } else if exact {
        println!("{}", ['1'].iter().cycle().take(size + 1).collect::<String>());
    } else {
        println!("{}", [first].iter().cycle().take(size).collect::<String>());
    }
}

fn main() {
    let stdin = io::stdin();
    let mut lines = stdin.lock().lines();
    let count = lines.next().unwrap().unwrap().parse::<usize>().unwrap();
    for line in lines.take(count) {
        suurempi(&line.unwrap());
    }
}

Test 1

Group: 1, 2

Verdict: WRONG ANSWER

Test 2

Group: 2

Verdict: WRONG ANSWER