day6

1 files changed, 105 insertions, 0 deletions

diff --git a/src/bin/day6.rs b/src/bin/day6.rs
new file mode 100644
index 0000000..67896e4
--- /dev/null
+++ b/src/bin/day6.rs
@@ -0,0 +1,105 @@
+use regex::Regex;
+
+fn main() {
+    let input = advent::read_lines(6);
+    println!("6a: {}", count_lit(&input));
+    println!("6b: {}", total_brightness(&input));
+}
+
+enum Operation {
+    Toggle,
+    TurnOn,
+    TurnOff,
+}
+
+struct Instruction {
+    op: Operation,
+    from: (usize, usize),
+    to: (usize, usize),
+}
+
+fn parse_instructions(input: &[String]) -> Vec<Instruction> {
+    let re = Regex::new(r"^([a-z ]+) (\d+),(\d+) through (\d+),(\d+)$").unwrap();
+    let mut instructions = Vec::new();
+    for line in input {
+        let cap = re.captures(line).unwrap();
+        let op = match &cap[1] {
+            "turn on" => Operation::TurnOn,
+            "turn off" => Operation::TurnOff,
+            "toggle" => Operation::Toggle,
+            err => panic!("unsupported operation: {}", err),
+        };
+        let x1 = cap[2].parse::<usize>().unwrap();
+        let y1 = cap[3].parse::<usize>().unwrap();
+        let x2 = cap[4].parse::<usize>().unwrap();
+        let y2 = cap[5].parse::<usize>().unwrap();
+        instructions.push(Instruction { op, from: (x1,y1), to: (x2,y2) });
+    }
+    instructions
+}
+
+fn decorations(input: &[String]) -> [[bool; 1000]; 1000] {
+    let instructions = parse_instructions(input);
+
+    let mut grid = [[false; 1000]; 1000];
+    for Instruction { op, from, to } in instructions {
+        for grid_x in grid.iter_mut().take(to.0 + 1).skip(from.0) {
+            for grid_x_y in grid_x.iter_mut().take(to.1 + 1).skip(from.1) {
+                *grid_x_y = match op {
+                    Operation::Toggle => !*grid_x_y,
+                    Operation::TurnOn => true,
+                    Operation::TurnOff => false,
+                };
+            }
+        }
+    }
+
+    grid
+}
+
+fn decorations2(input: &[String]) -> Vec<[i32; 1000]> {
+    let instructions = parse_instructions(input);
+
+    let mut grid = Vec::new();
+    for _ in 0..1000 {
+        grid.push([0; 1000]);
+    }
+    for Instruction { op, from, to } in instructions {
+        for grid_x in grid.iter_mut().take(to.0 + 1).skip(from.0) {
+            for grid_x_y in grid_x.iter_mut().take(to.1 + 1).skip(from.1) {
+                *grid_x_y = match op {
+                    Operation::Toggle => *grid_x_y + 2,
+                    Operation::TurnOn => *grid_x_y + 1,
+                    Operation::TurnOff => std::cmp::max(0, *grid_x_y - 1),
+                };
+            }
+        }
+    }
+
+    grid
+}
+
+fn count_lit(input: &[String]) -> usize {
+    decorations(input).iter()
+                      .flatten()
+                      .filter(|&x| *x)
+                      .count()
+}
+
+fn total_brightness(input: &[String]) -> i32 {
+    decorations2(input).iter()
+                       .flatten()
+                       .sum()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test() {
+        assert_eq!(count_lit(&["turn on 0,0 through 999,999".to_string()]), 1000 * 1000);
+        assert_eq!(total_brightness(&["turn on 0,0 through 0,0".to_string()]), 1);
+        assert_eq!(total_brightness(&["toggle 0,0 through 999,999".to_string()]), 2000000);
+    }
+}