scanner

Author: ia7ck

libs/scanner/Cargo.toml

@@ -0,0 +1,10 @@
+[package]
+name = "scanner"
+version = "0.1.0"
+authors = ["ia7ck <[email protected]>"]
+edition = "2021"
+license = "CC0-1.0"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

libs/scanner/src/lib.rs

@@ -0,0 +1,203 @@
+use std::{
+    fmt,
+    io::{self, BufReader, Cursor},
+    str,
+};
+
+pub struct Scanner<R>
+where
+    R: io::BufRead,
+{
+    reader: R,
+    buf: String,
+    pos: usize,
+}
+
+impl Scanner<BufReader<io::StdinLock<'static>>> {
+    /// Creates a scanner that reads from standard input.
+    pub fn stdin_lock() -> Self {
+        Self {
+            reader: BufReader::new(io::stdin().lock()),
+            buf: String::new(),
+            pos: 0,
+        }
+    }
+}
+
+impl<T> Scanner<Cursor<T>>
+where
+    T: AsRef<[u8]>,
+{
+    /// Creates a scanner that reads from a string or byte slice.
+    pub fn cursor(inner: T) -> Self {
+        Self {
+            reader: Cursor::new(inner),
+            buf: String::new(),
+            pos: 0,
+        }
+    }
+}
+
+impl<R> Scanner<R>
+where
+    R: io::BufRead,
+{
+    /// Scans and parses the next token from the input.
+    ///
+    /// For more convenient input scanning with variable declarations, see [`scan!`].
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use scanner::Scanner;
+    /// 
+    /// let mut scanner = Scanner::cursor("-10 20");
+    /// 
+    /// let x = scanner.scan::<i32>();
+    /// let y = scanner.scan::<i32>();
+    /// 
+    /// assert_eq!(x, -10);
+    /// assert_eq!(y, 20);
+    /// ```
+    pub fn scan<T>(&mut self) -> T
+    where
+        T: str::FromStr,
+        T::Err: fmt::Debug,
+    {
+        // skip whitespace
+        loop {
+            match self.buf[self.pos..].find(|ch| !char::is_ascii_whitespace(&ch)) {
+                Some(j) => {
+                    self.pos += j;
+                    break;
+                }
+                None => {
+                    let num_bytes = self
+                        .reader
+                        .read_line(&mut self.buf)
+                        .unwrap_or_else(|_| panic!("invalid UTF-8"));
+                    assert!(num_bytes > 0, "reached EOF :(");
+                }
+            }
+        }
+
+        let rest = &self.buf[self.pos..];
+        let token_len = rest
+            .find(|ch| char::is_ascii_whitespace(&ch))
+            .unwrap_or(rest.len());
+        let value = rest[..token_len]
+            .parse()
+            .unwrap_or_else(|e| panic!("{:?}, attempt to read `{}`", e, rest));
+        self.pos += token_len;
+
+        value
+    }
+}
+
+/// Macro for convenient input scanning with variable declarations.
+///
+/// For direct token scanning, see [`Scanner::scan()`].
+///
+/// # Examples
+///
+/// ```
+/// use scanner::{Scanner, scan};
+/// 
+/// let mut scanner = Scanner::cursor("3 10\n1 2 3");
+/// 
+/// scan! {
+///     via scanner,
+///     (n, k): (usize, usize),
+///     a: [i32; n],
+/// };
+/// 
+/// assert_eq!((n, k), (3, 10));
+/// assert_eq!(a, vec![1, 2, 3]);
+/// ```
+#[macro_export]
+macro_rules! scan {
+    (via $scanner:expr, $($rest:tt)*) => {
+        $crate::scan!(@via [$scanner] @rest $($rest)*);
+    };
+
+    (@via [$via:expr] @rest) => {};
+    (@via [$via:expr] @rest ,) => {};
+
+    (@via [$via:expr] @rest mut $($rest:tt)*) => {
+        $crate::scan!(@via [$via] @mut [mut] @rest $($rest)*);
+    };
+    (@via [$via:expr] @rest $($rest:tt)*) => {
+        $crate::scan!(@via [$via] @mut [] @rest $($rest)*);
+    };
+
+    (@via [$via:expr] @mut [$($mut:tt)?] @rest $var:tt : $t:tt) => {
+        let $($mut)? $var = $crate::scan_inner!(via $via, $t);
+    };
+    (@via [$via:expr] @mut [$($mut:tt)?] @rest $var:tt : $t:tt , $($rest:tt)*) => {
+        $crate::scan!(@via [$via] @mut [$($mut)?] @rest $var : $t);
+        $crate::scan!(@via [$via] @rest $($rest)*);
+    };
+}
+
+#[doc(hidden)]
+#[macro_export]
+macro_rules! scan_inner {
+    // (i32, i32)
+    (via $scanner:expr, ( $($t:tt),* )) => {
+        ( $($crate::scan_inner!(via $scanner, $t)),* )
+    };
+
+    // [i32; n]
+    (via $scanner:expr, [ $t:tt ; $len:expr ]) => {
+        ::std::iter::repeat_with(|| $crate::scan_inner!(via $scanner, $t)).take($len).collect::<Vec<_>>()
+    };
+
+    // i32
+    (via $scanner:expr, $ty:ty) => {
+        $scanner.scan::<$ty>()
+    };
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::Scanner;
+
+    #[test]
+    fn scan_test() {
+        let mut scanner = Scanner::cursor("42 123\n456\r\nABC");
+        assert_eq!(scanner.scan::<i32>(), 42);
+        assert_eq!(scanner.scan::<i32>(), 123);
+        assert_eq!(scanner.scan::<i32>(), 456);
+        assert_eq!(scanner.scan::<String>(), String::from("ABC"));
+    }
+
+    #[test]
+    fn scan_macro_test() {
+        let mut scanner = Scanner::cursor(
+            r#"
+3 10
+4
+1 2 3
+a 1
+b 2
+c 3
+d 4
+        "#,
+        );
+        scan! {
+            via scanner,
+            (n, k): (usize, usize),
+            mut q: usize,
+            a: [i32; n],
+            queries: [(char, i32); q],
+        };
+
+        assert_eq!((n, k), (3, 10));
+        assert_eq!(q, 4);
+        // test mutable
+        q += 1;
+        assert_eq!(q, 5);
+        assert_eq!(a, vec![1, 2, 3]);
+        assert_eq!(queries, vec![('a', 1), ('b', 2), ('c', 3), ('d', 4)]);
+    }
+}