Year 2016 Day 7

Author: maneatingape

README.md

@@ -249,6 +249,7 @@ pie
 | 4 | [Security Through Obscurity](https://adventofcode.com/2016/day/4) | [Source](src/year2016/day04.rs) | 75 |
 | 5 | [How About a Nice Game of Chess?](https://adventofcode.com/2016/day/5) | [Source](src/year2016/day05.rs) | 229000 |
 | 6 | [Signals and Noise](https://adventofcode.com/2016/day/6) | [Source](src/year2016/day06.rs) | 5 |
+| 7 | [Internet Protocol Version 7](https://adventofcode.com/2016/day/7) | [Source](src/year2016/day07.rs) | 354 |
 
 ## 2015
 

benches/benchmark.rs

@@ -70,6 +70,7 @@ mod year2016 {
     benchmark!(year2016, day04);
     benchmark!(year2016, day05);
     benchmark!(year2016, day06);
+    benchmark!(year2016, day07);
 }
 
 mod year2019 {

input/year2016/day07.txt

@@ -195,6 +195,7 @@ pub mod year2016 {
     pub mod day04;
     pub mod day05;
     pub mod day06;
+    pub mod day07;
 }
 
 /// # Rescue Santa from deep space with a solar system adventure.

src/lib.rs

@@ -108,6 +108,7 @@ fn all_solutions() -> Vec<Solution> {
         solution!(year2016, day04),
         solution!(year2016, day05),
         solution!(year2016, day06),
+        solution!(year2016, day07),
         // 2019
         solution!(year2019, day01),
         solution!(year2019, day02),

src/main.rs

@@ -0,0 +1,92 @@
+//! # Internet Protocol Version 7
+//!
+//! It's faster to treat the entire input as one big stream, using line breaks to increment
+//! the count if an address is valid.
+//!
+//! For part two there are at most 26 * 26 = 676 possible ABA or BAB sequences so we can use
+//! a fixed size array to keep track of which ones we've seen for the current address so far.
+pub fn parse(input: &str) -> &[u8] {
+    input.as_bytes()
+}
+
+pub fn part1(input: &[u8]) -> usize {
+    let mut count = 0;
+    let mut inside = false;
+    let mut positive = false;
+    let mut negative = false;
+
+    for w in input.windows(4) {
+        if w[0].is_ascii_lowercase() {
+            if w[0] == w[3] && w[1] == w[2] && w[0] != w[1] {
+                if inside {
+                    negative = true;
+                } else {
+                    positive = true;
+                }
+            }
+        } else if w[0] == b'[' {
+            inside = true;
+        } else if w[0] == b']' {
+            inside = false;
+        } else {
+            // Next line
+            if positive && !negative {
+                count += 1;
+            }
+            positive = false;
+            negative = false;
+        }
+    }
+
+    if positive && !negative {
+        count + 1
+    } else {
+        count
+    }
+}
+
+pub fn part2(input: &[u8]) -> usize {
+    let mut count = 0;
+    let mut version = 0;
+    let mut inside = false;
+    let mut positive = false;
+    let mut aba = [usize::MAX; 676];
+    let mut bab = [usize::MAX; 676];
+
+    for w in input.windows(3) {
+        if w[1].is_ascii_lowercase() {
+            if w[0] == w[2] && w[0] != w[1] {
+                let first = (w[0] - b'a') as usize;
+                let second = (w[1] - b'a') as usize;
+
+                if inside {
+                    // Reverse the order of letters
+                    let index = 26 * second + first;
+                    bab[index] = version;
+                    positive |= aba[index] == version;
+                } else {
+                    let index = 26 * first + second;
+                    aba[index] = version;
+                    positive |= bab[index] == version;
+                }
+            }
+        } else if w[1] == b'[' {
+            inside = true;
+        } else if w[1] == b']' {
+            inside = false;
+        } else {
+            // Next line
+            if positive {
+                count += 1;
+            }
+            version += 1;
+            positive = false;
+        }
+    }
+
+    if positive {
+        count + 1
+    } else {
+        count
+    }
+}

src/year2016/day07.rs

@@ -63,6 +63,7 @@ mod year2016 {
     mod day04_test;
     mod day05_test;
     mod day06_test;
+    mod day07_test;
 }
 
 mod year2019 {

tests/test.rs

@@ -0,0 +1,25 @@
+use aoc::year2016::day07::*;
+
+const FIRST_EXAMPLE: &str = "\
+abba[mnop]qrst
+abcd[bddb]xyyx
+aaaa[qwer]tyui
+ioxxoj[asdfgh]zxcvbn";
+
+const SECOND_EXAMPLE: &str = "\
+aba[bab]xyz
+xyx[xyx]xyx
+aaa[kek]eke
+zazbz[bzb]cdb";
+
+#[test]
+fn part1_test() {
+    let input = parse(FIRST_EXAMPLE);
+    assert_eq!(part1(input), 2);
+}
+
+#[test]
+fn part2_test() {
+    let input = parse(SECOND_EXAMPLE);
+    assert_eq!(part2(input), 3);
+}