Solution for 2022/day06-part2

2022/day06-part2/Cargo.toml

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+[package]
+name = "day06-part2"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

2022/day06-part2/src/main.rs

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+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");
+
+    // Define the length of characters that need to be unique.
+    // const N: usize = 4; // part one
+    const N: usize = 14; // part two
+
+    // Use a double-ended queue as a ringbuffer to keep track of the characters.
+    let mut deq = VecDeque::from([' '; N]);
+
+    // 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() >= N && !hs.contains(&' ') {
+            println!("Start of packet: {}", i + 1);
+            break;
+        }
+    }
+}