2018: day03: part 1

aoc2018/src/day03.rs

@@ -0,0 +1,103 @@
+use std::collections::HashMap;
+use std::fmt;
+
+use super::Result;
+
+const INPUT: &str = include_str!("../input/day03.txt");
+
+pub fn run() -> Result<()> {
+    println!("part 1: {}", part1(INPUT)?);
+
+    Ok(())
+}
+
+#[derive(Debug)]
+struct ParseError {
+    line: String,
+}
+
+impl ParseError {
+    fn new(line: &str) -> Self {
+        ParseError {
+            line: line.to_string(),
+        }
+    }
+}
+
+impl fmt::Display for ParseError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "{}", self.line)
+    }
+}
+
+impl std::error::Error for ParseError {
+    fn description(&self) -> &str {
+        &self.line
+    }
+}
+
+fn parse(line: &str) -> Option<(usize, usize, usize, usize)> {
+    // remove '#XXX @ ' start of line
+    let line = &line[(line.find(" @ ")? + 3)..];
+
+    // parse 'x,y: NNxNN
+    let comma = line.find(',')?;
+    let colon = line.find(':')?;
+    let x = line[..comma].parse().ok()?;
+    let y = line[(comma + 1)..colon].parse().ok()?;
+
+    // reduce line to 'NNxNN'
+    let line = &line[(colon + 2)..];
+
+    let sep = line.find('x')?;
+    let width = line[..sep].parse().ok()?;
+    let height = line[(sep + 1)..].parse().ok()?;
+
+    Some((x, y, width, height))
+}
+
+fn part1(input: &str) -> Result<u64> {
+    let mut res = 0;
+    let mut map: HashMap<(usize, usize), u64> = HashMap::default();
+
+    for line in input.lines() {
+        let (x, y, width, height) = parse(line).ok_or(ParseError::new(line))?;
+
+        for i in 0..width {
+            for j in 0..height {
+                let x = x + i;
+                let y = y + j;
+
+                // add tissue patch at coordinates (x, y)
+                let entry = map.entry((x, y)).or_default();
+                *entry += 1;
+
+                // count overlap the first time only
+                if *entry == 2 {
+                    res += 1;
+                }
+            }
+        }
+    }
+
+    Ok(res)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn part1_provided() {
+        let input = "#1 @ 1,3: 4x4
+#2 @ 3,1: 4x4
+#3 @ 5,5: 2x2
+";
+        assert_eq!(part1(input).unwrap(), 4);
+    }
+
+    #[test]
+    fn part1_real() {
+        assert_eq!(part1(INPUT).unwrap(), 114946);
+    }
+}

aoc2018/src/lib.rs

@@ -1,4 +1,5 @@
 pub mod day01;
 pub mod day02;
+pub mod day03;
 
 pub type Result<T> = std::result::Result<T, Box<dyn std::error::Error>>;