31 lines
1.2 KiB
Rust
31 lines
1.2 KiB
Rust
use std::collections::{HashSet, VecDeque};
|
|
|
|
fn main() {
|
|
// Use command line arguments to specify the input filename.
|
|
let args: Vec<String> = std::env::args().collect();
|
|
if args.len() < 2 {
|
|
panic!("Usage: ./main <input-file>\nNo input file provided. Exiting.");
|
|
}
|
|
|
|
// Next, read the contents of the input file into a string for easier processing.
|
|
let input = std::fs::read_to_string(&args[1]).expect("Error opening file");
|
|
|
|
// Use a double-ended queue as a ringbuffer to keep track of the characters.
|
|
let mut deq = VecDeque::from([' '; 4]);
|
|
|
|
// Iterate through all characters, together with their respective indices.
|
|
for (i, char) in input.chars().enumerate() {
|
|
// Remove the first character from the deque.
|
|
deq.pop_front();
|
|
// And add the next character to it.
|
|
deq.push_back(char);
|
|
// Collecting into a set, removing duplicates along the way.
|
|
let hs: HashSet<char> = deq.iter().copied().collect();
|
|
// Count the number of unique elements in the set.
|
|
if hs.len() >= 4 && !hs.contains(&' ') {
|
|
println!("Start of packet: {}", i + 1);
|
|
break;
|
|
}
|
|
}
|
|
}
|