1 files changed, 119 insertions, 0 deletions
diff --git a/2016/src/bin/day07.rs b/2016/src/bin/day07.rs
new file mode 100644
index 0000000..b4967ff
--- /dev/null
+++ b/2016/src/bin/day07.rs
@@ -0,0 +1,119 @@
+use std::io::{self, Read};
+use std::str::FromStr;
+
+fn has_abba(s: &str) -> bool {
+    s.as_bytes()
+        .windows(4)
+        .any(|window| {
+            window[0] == window[3]
+                && window[1] == window[2]
+                && window[0] != window[1]
+        })
+}
+
+fn abas(s: &str) -> Vec<&[u8]> {
+    s.as_bytes()
+        .windows(3)
+        .filter(|window| {
+            window[0] == window[2]
+                && window[0] != window[1]
+        })
+        .collect()
+}
+
+fn has_bab(s: &str, aba: &[u8]) -> bool {
+    s.as_bytes()
+        .windows(3)
+        .any(|window| {
+            window[0] == aba[1]
+                && window[1] == aba[0]
+                && window[2] == aba[1]
+        })
+}
+
+#[derive(Default)]
+struct Ip {
+    supernet: Vec<String>,
+    hypernet: Vec<String>,
+}
+
+impl Ip {
+    fn supports_tls(&self) -> bool {
+        self.supernet.iter().any(|s| has_abba(s))
+            && !self.hypernet.iter().any(|s| has_abba(s))
+    }
+
+    fn supports_ssl(&self) -> bool {
+        self.supernet
+            .iter()
+            .flat_map(|s| abas(s))
+            .any(|aba| {
+                self.hypernet
+                    .iter()
+                    .any(|s| has_bab(s, aba))
+            })
+    }
+}
+
+impl FromStr for Ip {
+    type Err = ();
+    fn from_str(s: &str) -> Result<Ip, ()> {
+        let mut ip = Ip::default();
+
+        for (i, seq) in s.split(|ch| ch == '[' || ch == ']').enumerate() {
+            if i % 2 == 0 {
+                ip.supernet.push(seq.to_owned());
+            } else {
+                ip.hypernet.push(seq.to_owned());
+            }
+        }
+
+        Ok(ip)
+    }
+}
+
+fn solve1(input: &str) -> usize {
+    input.lines()
+        .map(str::parse)
+        .map(Result::unwrap)
+        .filter(Ip::supports_tls)
+        .count()
+}
+
+fn solve2(input: &str) -> usize {
+    input.lines()
+        .map(str::parse)
+        .map(Result::unwrap)
+        .filter(Ip::supports_ssl)
+        .count()
+}
+
+fn main() {
+    let mut input = String::new();
+    io::stdin().read_to_string(&mut input).unwrap();
+
+    println!("Part 1: {}", solve1(&input));
+    println!("Part 2: {}", solve2(&input));
+}
+
+#[test]
+fn part1() {
+    let input = "
+abba[mnop]qrst
+abcd[bddb]xyyx
+aaaa[qwer]tyui
+ioxxoj[asdfgh]zxcvbn
+";
+    assert_eq!(2, solve1(input.trim()));
+}
+
+#[test]
+fn part2() {
+    let input = "
+aba[bab]xyz
+xyx[xyx]xyx
+aaa[kek]eke
+zazbz[bzb]cdb
+";
+    assert_eq!(3, solve2(input.trim()));
+}