Solution to https://open.kattis.com/problems/substitution (fails second secret test case)

Substitution.rs

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

fn main() {
    // Get the input as an iterator
    // Transforms each line of input, a string containing a sequence of numbers
    // (indexed from one) into a vector of i64, all indexed from zero
    let stdin = io::stdin();
    let is =
        stdin
        .lock()
        .lines()
        .map(|l| l
            .unwrap() // Input is well-formed, no need for exception handling
            .split_whitespace()
            .map(|num_as_str| num_as_str.parse().unwrap())
            .map(|num: i64| num - 1) // zero-index the numbers
            .collect() // collect to a vector
        );

    // Skip the number of test cases
    let mut it = is.into_iter().skip(1);

    // Let binding allows us to skip the first line of the test case while also ensuring
    // that we have more test cases to process -- nice!
    while let Some(_) = it.next() {
        let mut num_cycles: i32 = 0;
        let mut ms: Vec<i64> = it.next().unwrap();
        let cs: Vec<i64> = it.next().unwrap();
        let ps: Vec<i64> = it.next().unwrap();

        while !ms.eq(&cs) {
            for i in 0..ms.len() {
                ms[i] = ps[ms[i] as usize]
            }
            num_cycles += 1
        }
        println!("{:?}", num_cycles)
    }
}