Monistus

warning: variable does not need to be mutable
  --> input/code.rs:13:9
   |
13 |     let mut i: usize = 0;
   |         ----^
   |         |
   |         help: remove this `mut`
   |
   = note: `#[warn(unused_mut)]` on by default

warning: variable does not need to be mutable
  --> input/code.rs:22:21
   |
22 |                 let mut duplicate_times = 2;
   |                     ----^^^^^^^^^^^^^^^
   |                     |
   |                     help: remove this `mut`

warning: variable does not need to be mutable
  --> input/code.rs:40:14
   |
40 | fn duplicate(mut substring: VecDeque<char>, times: u32) -> VecDeque<char> {
   |              ----^^^^^^^^^
   |              |
   |              help: remove this `mut`

warning: 3 warnings emitted

use std::collections::VecDeque;

fn main() {
    let mut input: String = String::new();
    std::io::stdin().read_line(&mut input).unwrap();
    input = input.strip_suffix("\n").unwrap().to_string();

    println!("{}", process(input.chars().collect()))
}

fn process(mut input: VecDeque<char>) -> String {
    let mut output = String::new();
    let mut i: usize = 0;
    while i < input.len() {
        let character = input.pop_front().unwrap();

        match character.to_digit(10) {
            None => {
                output.push(character);
            }
            Some(len) => {
                let mut duplicate_times = 2;

                let capture = input.drain(i .. i + len as usize).collect(); // Remove duplicated area

                let mut duplicate = duplicate(capture, duplicate_times);

                // Put back in duplicated form
                let duplicate_length = duplicate.len();
                for _ in 0..duplicate_length {
                    input.insert(i, duplicate.pop_back().unwrap())
                }
            }
        }
    }

    return output;
}

fn duplicate(mut substring: VecDeque<char>, times: u32) -> VecDeque<char> {
    // Is this seriously the best way to do this in Rust?
    let mut out = VecDeque::new();
    for _ in 0..times {
        out.append(&mut substring.clone());
    }
    return out
}

Test 1

Group: 1, 2

Verdict: ACCEPTED

Test 2

Group: 1, 2

Verdict: ACCEPTED

Test 3

Group: 1, 2

Verdict: ACCEPTED

Test 4

Group: 1, 2

Verdict: ACCEPTED

Test 5

Group: 1, 2

Verdict: ACCEPTED

Test 6

Group: 1, 2

Verdict: ACCEPTED

Test 7

Group: 1, 2

Verdict: ACCEPTED

Test 8

Group: 2

Verdict: ACCEPTED

Test 9

Group: 2

Verdict: ACCEPTED

Test 10

Group: 2

Verdict: ACCEPTED

Test 11

Group: 2

Verdict: ACCEPTED

Test 12

Group: 2

Verdict: ACCEPTED

Test 13

Group: 2

Verdict: ACCEPTED

Test 14

Group: 2

Verdict: ACCEPTED