cleanup

2023/day10/src/lib.rs

@@ -59,6 +59,19 @@ enum Direction {
     None,
 }
 
+fn left(pos: usize, width: usize) -> Option<usize> {
+    (pos % width > 0).then(|| pos - 1)
+}
+fn right(pos: usize, width: usize) -> Option<usize> {
+    ((pos % width) < (width - 1)).then(|| pos + 1)
+}
+fn top(pos: usize, width: usize) -> Option<usize> {
+    (pos >= width).then(|| pos - width)
+}
+fn bottom(pos: usize, len: usize, width: usize) -> Option<usize> {
+    (pos < (len - width)).then(|| pos + width)
+}
+
 impl Candidates<'_> {
     fn push(&mut self, new: Candidate) {
         match (new.came_from, self.bytes[new.pos]) {
@@ -71,39 +84,31 @@ impl Candidates<'_> {
     }
 
     fn push_left(&mut self, from: Candidate) {
-        if from.came_from != Direction::Left && from.pos % self.width > 0 {
+        if from.came_from != Direction::Left {
-            self.push(Candidate::new(
+            if let Some(left) = left(from.pos, self.width) {
-                from.count + 1,
+                self.push(Candidate::new(from.count + 1, left, Direction::Right));
-                from.pos - 1,
+            }
-                Direction::Right,
-            ));
         }
     }
     fn push_right(&mut self, from: Candidate) {
-        if from.came_from != Direction::Right && (from.pos % self.width) < (self.width - 1) {
+        if from.came_from != Direction::Right {
-            self.push(Candidate::new(
+            if let Some(right) = right(from.pos, self.width) {
-                from.count + 1,
+                self.push(Candidate::new(from.count + 1, right, Direction::Left));
-                from.pos + 1,
+            }
-                Direction::Left,
-            ));
         }
     }
     fn push_top(&mut self, from: Candidate) {
-        if from.came_from != Direction::Top && from.pos >= self.width {
+        if from.came_from != Direction::Top {
-            self.push(Candidate::new(
+            if let Some(top) = top(from.pos, self.width) {
-                from.count + 1,
+                self.push(Candidate::new(from.count + 1, top, Direction::Bottom));
-                from.pos - self.width,
+            }
-                Direction::Bottom,
-            ));
         }
     }
     fn push_bottom(&mut self, from: Candidate) {
-        if from.came_from != Direction::Bottom && from.pos < (self.len - self.width) {
+        if from.came_from != Direction::Bottom {
-            self.push(Candidate::new(
+            if let Some(bottom) = bottom(from.pos, self.bytes.len(), self.width) {
-                from.count + 1,
+                self.push(Candidate::new(from.count + 1, bottom, Direction::Top));
-                from.pos + self.width,
+            }
-                Direction::Top,
-            ));
         }
     }
 }
@@ -247,12 +252,14 @@ fn part1(input: &str) -> u64 {
     get_loop(input).highest_value
 }
 
-fn part2(_input: &str) -> u64 {
+fn part2(input: &str) -> u64 {
     // Step 1: Find the loop
     //         We do this by using the step-map from before, counting backwards from the target basically.
     // Step 2: Cellular-automata-ish, start from the borders and start eating away
     //         everything connected to that, only stopping at the main loop.
     // Open question: How do we squeeze between main loop pipes?
+    let the_loop = get_loop(input);
+    let mut tiles = vec![0; the_loop.step_map.len()];
 
     0
 }

file.rs

@@ -0,0 +1,75 @@
+use std::ops::Add;
+
+fn parse(input: &str, into: &mut Vec<i64>, mut line_callback: impl FnMut(&mut Vec<i64>)) {
+    let mut neg = false;
+    let mut acc = 0;
+
+    for byte in input.bytes() {
+        match byte {
+            b' ' => {
+                if neg {
+                    acc = -acc
+                };
+                into.push(acc);
+                acc = 0;
+                neg = false;
+            }
+            b'-' => neg = true,
+            b'\n' => {
+                if neg {
+                    acc = -acc
+                };
+                into.push(acc);
+                line_callback(into);
+                into.clear();
+                acc = 0;
+                neg = false;
+            }
+            // must be b'0'..=b'9'
+            _ => {
+                let value = byte - b'0';
+                acc = (acc * 10) + (value as i64);
+            }
+        }
+    }
+}
+
+fn execute(
+    input: &str,
+    last_or_first: impl Fn(&[i64]) -> i64,
+    fold: impl Fn(i64, i64) -> i64 + Copy,
+) -> i64 {
+    let mut row1 = Vec::with_capacity(128);
+    let mut row2 = Vec::with_capacity(128);
+
+    let mut last_values = Vec::with_capacity(16);
+
+    let mut total = 0;
+
+    parse(input, &mut row1, |row1| {
+        row2.clone_from(&row1);
+
+        last_values.clear();
+        last_values.push(last_or_first(&row1));
+        while !row2.iter().all(|&n| n == 0) {
+            row1.clear();
+            row1.extend(row2.windows(2).map(|s| s[1] - s[0]));
+
+            last_values.push(last_or_first(&row1));
+
+            std::mem::swap(row1, &mut row2);
+        }
+
+        total += last_values.iter().copied().rev().fold(0, fold);
+    });
+
+    total
+}
+
+pub fn run(input: &str) -> u64 {
+    execute(input, |s| *s.last().unwrap(), Add::add) as u64
+}
+
+pub fn part2(input: &str) -> u64 {
+    execute(input, |s| *s.first().unwrap(), |a, b| b - a) as u64
+}