1 files changed, 80 insertions, 0 deletions
diff --git a/src/bin/day11.rs b/src/bin/day11.rs
new file mode 100644
index 0000000..b945c73
--- /dev/null
+++ b/src/bin/day11.rs
@@ -0,0 +1,80 @@
+use std::collections::HashSet;
+
+fn main() {
+    let input = "hxbxwxba";
+    println!("11a: {}", next_password(input));
+    println!("11b: {}", next_password(&next_password(input)));
+}
+
+fn has_straight(password: &str) -> bool {
+    let mut prevprev = password.chars().next().unwrap().to_digit(36).unwrap();
+    let mut prev = password.chars().nth(1).unwrap().to_digit(36).unwrap();
+
+    for c in password.chars().skip(2) {
+        let digit = c.to_digit(36).unwrap();
+        if prevprev + 1 == prev && prev + 1 == digit {
+            return true;
+        }
+        prevprev = prev;
+        prev = digit;
+    }
+    false
+}
+
+fn has_forbidden_letters(password: &str) -> bool {
+    password.contains('i') || password.contains('o') || password.contains('l')
+}
+
+fn has_two_pairs(password: &str) -> bool {
+    let mut pairs = HashSet::new();
+    let mut prev = password.chars().next().unwrap();
+
+    for c in password.chars().skip(1) {
+        if prev == c {
+            pairs.insert(c);
+        }
+        prev = c;
+    }
+    pairs.len() > 1
+}
+
+fn valid_password(password: &str) -> bool {
+    has_straight(password) && !has_forbidden_letters(password) && has_two_pairs(password)
+}
+
+fn inc_password_at_position(password: &str, pos: usize) -> String {
+    let mut bytes = password.to_string().into_bytes();
+    bytes.reverse();
+    bytes[pos] += 1;
+    if bytes[pos] > b'z' {
+        bytes[pos] = b'a';
+        bytes.reverse();
+        let new_password = String::from_utf8(bytes.to_vec()).unwrap();
+        inc_password_at_position(&new_password, pos + 1)
+    } else {
+        bytes.reverse();
+        String::from_utf8(bytes.to_vec()).unwrap()
+    }
+}
+
+fn next_password(password: &str) -> String {
+    let mut password = inc_password_at_position(password, 0);
+    while !valid_password(&password) {
+        password = inc_password_at_position(&password, 0)
+    }
+    password
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test() {
+        assert!(!valid_password("hijklmmn"));
+        assert!(!valid_password("abbceffg"));
+        assert!(!valid_password("abbcegjk"));
+        assert_eq!(next_password("abcdefgh"), "abcdffaa");
+        assert_eq!(next_password("ghijklmn"), "ghjaabcc");
+    }
+}