y2016d4

y2016/src/days/d4.rs

@@ -0,0 +1,119 @@
+use std::collections::HashMap;
+
+pub fn process_part1(input: &str) -> u32 {
+    input
+        .lines()
+        .map(|line| {
+            let name = get_name(line);
+            let id = get_id(line);
+            let checksum = get_checksum(line);
+            let stats = get_freq_and_position(&name);
+            let mut sorted_stats = stats.into_iter().collect::<Vec<(char, i32)>>();
+            sorted_stats.sort_by(|(a, a_freq), (b, b_freq)| match b_freq.cmp(a_freq) {
+                std::cmp::Ordering::Less => std::cmp::Ordering::Less,
+                std::cmp::Ordering::Greater => std::cmp::Ordering::Greater,
+                std::cmp::Ordering::Equal => a.cmp(b),
+            });
+            for (char, _stats) in sorted_stats.into_iter().take(5) {
+                if !checksum.contains(char) {
+                    return 0;
+                }
+            }
+            id
+        })
+        .sum()
+}
+
+pub fn process_part2(input: &str) -> String {
+    input
+        .lines()
+        .filter(|line| {
+            let name = get_name(line);
+            let checksum = get_checksum(line);
+            let stats = get_freq_and_position(&name);
+            let mut sorted_stats = stats.into_iter().collect::<Vec<(char, i32)>>();
+            sorted_stats.sort_by(|(a, a_freq), (b, b_freq)| match b_freq.cmp(a_freq) {
+                std::cmp::Ordering::Less => std::cmp::Ordering::Less,
+                std::cmp::Ordering::Greater => std::cmp::Ordering::Greater,
+                std::cmp::Ordering::Equal => a.cmp(b),
+            });
+            for (char, _stats) in sorted_stats.into_iter().take(5) {
+                if !checksum.contains(char) {
+                    return false;
+                }
+            }
+            true
+        })
+        .map(|line| {
+            let name = get_name(line);
+            let id = get_id(line);
+            format!("{}: {id}", rot(&name, id))
+        })
+        .collect::<Vec<String>>()
+        .join("\n")
+}
+
+fn rot(name: &str, count: u32) -> String {
+    let mut decrypted = Vec::new();
+    for &byte in name.as_bytes() {
+        if byte == b'-' {
+            decrypted.push(b' ');
+            continue;
+        }
+        let shift = (byte - b'a') as u32 + count;
+        decrypted.push((shift % 26) as u8 + b'a');
+    }
+    String::from_utf8(decrypted).unwrap()
+}
+
+fn get_name(room: &str) -> String {
+    room.rsplit_once("-").unwrap().0.to_string()
+}
+
+fn get_id(room: &str) -> u32 {
+    let id_start = room.rfind("-").unwrap() + 1;
+    let id_end = room.find("[").unwrap();
+    room[id_start..id_end].parse().unwrap()
+}
+
+fn get_checksum(room: &str) -> String {
+    let id_start = room.find("[").unwrap() + 1;
+    room[id_start..room.len() - 1].to_string()
+}
+
+fn get_freq_and_position(name: &str) -> HashMap<char, i32> {
+    let mut freq = HashMap::new();
+    for char in name.chars() {
+        if char == '-' {
+            continue;
+        }
+        freq.entry(char)
+            .and_modify(|count| {
+                *count += 1;
+            })
+            .or_insert(1);
+    }
+    freq
+}
+
+#[cfg(test)]
+mod tests {
+    use super::{rot, *};
+
+    const INPUT: &str = "aaaaa-bbb-z-y-x-123[abxyz]
+a-b-c-d-e-f-g-h-987[abcde]
+not-a-real-room-404[oarel]
+totally-real-room-200[decoy]";
+
+    #[test]
+    fn part1() {
+        let result = process_part1(INPUT);
+        assert_eq!(result, 1514);
+    }
+
+    #[test]
+    fn part2() {
+        let res = rot("qzmt-zixmtkozy-ivhz", 343);
+        assert_eq!(res, "very encrypted name".to_string());
+    }
+}

y2016/src/days/mod.rs

@@ -3,3 +3,5 @@ pub mod d1;
 pub mod d2;
 
 pub mod d3;
+
+pub mod d4;