feat: add day 6

data/examples/06.txt

@@ -0,0 +1,16 @@
+eedadn
+drvtee
+eandsr
+raavrd
+atevrs
+tsrnev
+sdttsa
+rasrtv
+nssdts
+ntnada
+svetve
+tesnvt
+vntsnd
+vrdear
+dvrsen
+enarar

src/bin/05.rs

@@ -1,8 +1,7 @@
 advent_of_code::solution!(5);
 
 fn get_valid_digests(prefix: &str) -> impl Iterator<Item = String> + '_ {
-    (1..)
+    (1..).flat_map(move |x| {
-        .flat_map(move |x| {
         let data = format!("{}{:?}", prefix, x);
         let digest = format!("{:x}", md5::compute(data));
         if digest.starts_with("00000") {

src/bin/06.rs

@@ -0,0 +1,65 @@
+advent_of_code::solution!(6);
+
+use std::collections::HashMap;
+
+fn compute_frequencies(input: &str) -> HashMap<usize, HashMap<char, usize>> {
+    let frequencies: HashMap<usize, HashMap<char, usize>> = HashMap::new();
+    input.split("\n").fold(frequencies, |mut frq, str| {
+        str.chars().enumerate().for_each(|(n, c)| {
+            let slot_frq = frq.entry(n).or_default();
+            *slot_frq.entry(c).or_default() += 1;
+        });
+        frq
+    })
+}
+
+pub fn part_one(input: &str) -> Option<String> {
+    let input = input.strip_suffix("\n").unwrap_or(input);
+    let mut res = compute_frequencies(input)
+        .into_iter()
+        .map(|(k, v)| {
+            (
+                k,
+                v.into_iter()
+                    .max_by_key(|(_, cnt)| *cnt)
+                    .map(|(chr, _)| chr),
+            )
+        })
+        .collect::<Vec<_>>();
+    res.sort_by_key(|(k, _)| *k);
+    Some(res.into_iter().map(|(_, v)| v.unwrap()).collect::<String>())
+}
+
+pub fn part_two(input: &str) -> Option<String> {
+    let input = input.strip_suffix("\n").unwrap_or(input);
+    let mut res = compute_frequencies(input)
+        .into_iter()
+        .map(|(k, v)| {
+            (
+                k,
+                v.into_iter()
+                    .min_by_key(|(_, cnt)| *cnt)
+                    .map(|(chr, _)| chr),
+            )
+        })
+        .collect::<Vec<_>>();
+    res.sort_by_key(|(k, _)| *k);
+    Some(res.into_iter().map(|(_, v)| v.unwrap()).collect::<String>())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_part_one() {
+        let result = part_one(&advent_of_code::template::read_file("examples", DAY));
+        assert_eq!(result, Some("easter".into()));
+    }
+
+    #[test]
+    fn test_part_two() {
+        let result = part_two(&advent_of_code::template::read_file("examples", DAY));
+        assert_eq!(result, Some("advent".into()));
+    }
+}