1 files changed, 89 insertions, 0 deletions
diff --git a/src/bin/day8.rs b/src/bin/day8.rs
new file mode 100644
index 0000000..725f129
--- /dev/null
+++ b/src/bin/day8.rs
@@ -0,0 +1,89 @@
+fn main() {
+    let input = advent::read_lines(8);
+    println!("8a: {}", count_chars_decoding(&input));
+    println!("8b: {}", count_chars_encoding(&input));
+}
+
+fn decode_string(word: &str) -> Vec<u8> {
+    let mut decoded = Vec::new();
+
+    let mut chars = word.chars();
+    // drop " at beginning
+    assert_eq!(chars.next(), Some('"'));
+
+    while let Some(c) = chars.next() {
+        if c == '\\' {
+            let next = chars.next().unwrap();
+            if next == 'x' {
+                let digit1 = chars.next().unwrap().to_digit(16).unwrap();
+                let digit2 = chars.next().unwrap().to_digit(16).unwrap();
+                let code = 16 * digit1 + digit2;
+                decoded.push(char::from_u32(code).unwrap() as u8);
+            } else {
+                decoded.push(next as u8);
+            }
+        } else {
+            decoded.push(c as u8);
+        }
+    }
+
+    // drop " at end
+    assert_eq!(decoded.pop(), Some(34));
+
+    decoded
+}
+
+fn count_chars_decoding<T: AsRef<str>>(input: &[T]) -> usize {
+    let mut code = 0;
+    let mut values = 0;
+
+    for line in input {
+        code += line.as_ref().len();
+        values += decode_string(line.as_ref()).len();
+    }
+    code - values
+}
+
+fn encode_string(word: &str) -> String {
+    let mut encoded = String::new();
+    encoded.push('"');
+
+    for c in word.chars() {
+        match c {
+            '"' => encoded += "\\\"",
+            '\\' => encoded += "\\\\",
+            rest => encoded.push(rest),
+        }
+    }
+
+    encoded.push('"');
+    encoded
+}
+
+fn count_chars_encoding<T: AsRef<str>>(input: &[T]) -> usize {
+    let mut code = 0;
+    let mut values = 0;
+
+    for line in input {
+        code += line.as_ref().len();
+        values += encode_string(line.as_ref()).len();
+    }
+    values - code
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test() {
+        let input = [
+            "\"\"",
+            "\"abc\"",
+            "\"aaa\\\"aaa\"",
+            "\"\\x27\"",
+        ];
+        assert_eq!(count_chars_decoding(&input), 12);
+        assert_eq!(count_chars_encoding(&input), 19);
+    }
+}