From d002880b830389144868e875dd42f948de8cdd83 Mon Sep 17 00:00:00 2001
From: Fabian Schmidt <fabschmidt96@gmail.com>
Date: Tue, 29 Oct 2024 14:36:36 +0100
Subject: [PATCH] y2015d11

---
 y2015/src/bin/d11.rs  | 14 +++++++++
 y2015/src/days/d11.rs | 70 +++++++++++++++++++++++++++++++++++++++++++
 y2015/src/days/mod.rs |  1 +
 3 files changed, 85 insertions(+)
 create mode 100644 y2015/src/bin/d11.rs
 create mode 100644 y2015/src/days/d11.rs

diff --git a/y2015/src/bin/d11.rs b/y2015/src/bin/d11.rs
new file mode 100644
index 0000000..e431d6b
--- /dev/null
+++ b/y2015/src/bin/d11.rs
@@ -0,0 +1,14 @@
+use y2015::days::d11;
+
+fn main() {
+    part1();
+    part2();
+}
+
+fn part1() {
+    println!("{}", d11::process_part1("hepxcrrq"));
+}
+
+fn part2() {
+    println!("{}", d11::process_part1(&d11::process_part1("hepxcrrq")));
+}
diff --git a/y2015/src/days/d11.rs b/y2015/src/days/d11.rs
new file mode 100644
index 0000000..1d563c8
--- /dev/null
+++ b/y2015/src/days/d11.rs
@@ -0,0 +1,70 @@
+pub fn process_part1(input: &str) -> String {
+    let mut password = input.to_string();
+    loop {
+        password = increment(&password);
+        if password.contains("i") || password.contains("o") || password.contains("l") {
+            continue;
+        }
+        if !has_straight(&password) {
+            continue;
+        }
+        if num_pairs(&password) < 2 {
+            continue;
+        }
+        return password;
+    }
+}
+
+fn has_straight(password: &str) -> bool {
+    for window in password.as_bytes().windows(3) {
+        let (a, b, c) = (window[0], window[1], window[2]);
+        let (inc_b, inc_c) = (increment_letter(a), increment_letter(b));
+        if b == inc_b.0 && c == inc_c.0 && !(inc_b.1 || inc_c.1) {
+            return true;
+        }
+    }
+    false
+}
+
+fn num_pairs(password: &str) -> u32 {
+    let mut num_pairs = 0;
+    let mut was_last_pair = false;
+    password.as_bytes().windows(2).for_each(|window| {
+        if window[0] == window[1] && !was_last_pair {
+            num_pairs += 1;
+            was_last_pair = true;
+        } else {
+            was_last_pair = false;
+        }
+    });
+    num_pairs
+}
+
+fn increment(password: &str) -> String {
+    let mut password_bytes = password.as_bytes().to_vec();
+    password_bytes.reverse();
+    let mut new_password_bytes = vec![];
+    let mut increment_next = true;
+    for letter in password_bytes {
+        if increment_next {
+            let (new_letter, overflow) = increment_letter(letter);
+            new_password_bytes.push(new_letter);
+            increment_next = overflow;
+        } else {
+            new_password_bytes.push(letter);
+        }
+    }
+    if increment_next {
+        new_password_bytes.push(b'a');
+    }
+    new_password_bytes.reverse();
+    String::from_utf8(new_password_bytes).unwrap()
+}
+
+fn increment_letter(letter: u8) -> (u8, bool) {
+    if letter == b'z' {
+        (b'a', true)
+    } else {
+        (letter + 1, false)
+    }
+}
diff --git a/y2015/src/days/mod.rs b/y2015/src/days/mod.rs
index ab0515c..45f3d0b 100644
--- a/y2015/src/days/mod.rs
+++ b/y2015/src/days/mod.rs
@@ -1,5 +1,6 @@
 pub mod d1;
 pub mod d10;
+pub mod d11;
 pub mod d2;
 pub mod d3;
 pub mod d4;