Merge pull request #1 from rust-munich/solutions/sven

solution(sven): providing my ugly custom iterator solution

Author: sassman

solutions/sven/Cargo.toml

@@ -0,0 +1,6 @@
+[package]
+name = "sven"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]

solutions/sven/src/lib.rs

@@ -0,0 +1,150 @@
+struct Grid {
+    cells: Vec<Vec<char>>,
+}
+
+impl Grid {
+    fn new(input: &str) -> Self {
+        Self {
+            cells: input.lines().map(|l| l.trim().chars().collect()).collect(),
+        }
+    }
+
+    fn width(&self) -> usize {
+        self.cells.first().map_or(0, |r| r.len())
+    }
+
+    fn height(&self) -> usize {
+        self.cells.len()
+    }
+
+    fn get(&self, row: usize, col: usize) -> Option<char> {
+        self.cells.get(row)?.get(col).copied()
+    }
+
+    fn paperolls(&self) -> PaperrollIterator {
+        PaperrollIterator {
+            grid: self,
+            current_row: 0,
+            current_col: 0,
+        }
+    }
+}
+
+struct PaperrollIterator<'a> {
+    grid: &'a Grid,
+    current_row: usize,
+    current_col: usize,
+}
+
+impl Iterator for PaperrollIterator<'_> {
+    type Item = (usize, usize, char);
+
+    fn next(&mut self) -> Option<Self::Item> {
+        loop {
+            if self.current_row >= self.grid.height() {
+                return None;
+            }
+            if self.current_col >= self.grid.width() {
+                self.current_col = 0;
+                self.current_row += 1;
+                continue;
+            }
+
+            let (x, y) = (self.current_row, self.current_col);
+            let c = self.grid.get(x, y)?;
+
+            if c != '@' {
+                // no paperroll here, continue
+                self.current_col += 1;
+                continue;
+            }
+
+            // we are at (x, y) with '@', so we check now all the neighbors,
+            // if a neigboar is also '@', we count it,
+            // if the count is >= 4 we continue the loop on the next position
+
+            let mut paperrolls = 0;
+            for dx in -1..=1 {
+                for dy in -1..=1 {
+                    if dx == 0 && dy == 0 {
+                        continue;
+                    }
+                    let nx = x as isize + dx;
+                    let ny = y as isize + dy;
+                    if nx >= 0 && ny >= 0 {
+                        if let Some(nc) = self.grid.get(nx as usize, ny as usize) {
+                            if nc == '@' {
+                                paperrolls += 1;
+                            }
+                        }
+                    }
+
+                    if paperrolls >= 4 {
+                        break;
+                    }
+                }
+            }
+
+            self.current_col += 1;
+            if paperrolls >= 4 {
+                continue; // this was not a valid paperroll
+            }
+            // else we found a valid paperroll
+            return Some((x, y, c));
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn grid() -> Grid {
+        Grid::new(
+            r#"..@@.@@@@.
+        @@@.@.@.@@
+        @@@@@.@.@@
+        @.@@@@..@.
+        @@.@@@@.@@
+        .@@@@@@@.@
+        .@.@.@.@@@
+        @.@@@.@@@@
+        .@@@@@@@@.
+        @.@.@@@.@."#,
+        )
+    }
+
+    #[test]
+    fn test_grid() {
+        let g = grid();
+
+        assert_eq!(g.height(), 10);
+        assert_eq!(g.width(), 10);
+
+        assert_eq!(g.get(0, 0), Some('.'));
+        assert_eq!(g.get(0, 2), Some('@'));
+        assert_eq!(g.get(1, 0), Some('@'));
+        assert_eq!(g.get(1, 3), Some('.'));
+        assert_eq!(g.get(1, 4), Some('@'));
+        assert_eq!(g.get(9, 9), Some('.'));
+        assert_eq!(g.get(10, 0), None);
+    }
+
+    #[test]
+    fn test_iterator() {
+        let g = grid();
+
+        for (x, y, c) in g.paperolls() {
+            println!("({x}, {y}) = {c}");
+        }
+
+        assert_eq!(g.paperolls().count(), 13);
+    }
+
+    #[test]
+    fn test_input_final() {
+        let g = Grid::new(include_str!("../../../input.txt"));
+        let paperrolls = g.paperolls().count();
+        println!("Paperolls = {paperrolls}");
+    }
+}