hmm

aoc2023/src/day11.rs

@@ -1,13 +1,55 @@
 use shared::{Solution, Answer};
+use itertools::Itertools;
 
 pub struct Day11;
 
 impl Solution for Day11 {
     fn part_1(&self, input: &str) -> Answer {
-        Answer::Unimplemented
+        Answer::from(solve(input, 2))
     }
 
     fn part_2(&self, input: &str) -> Answer {
-        Answer::Unimplemented
+        Answer::from(solve(input, 1_000_000))
     }
 }
+
+fn solve(input: &str, inflation_arg: usize) -> u64 {
+    let grid = input.lines().map(|line| line.chars().map(|x| x == '#').collect::<Vec<bool>>()).collect::<Vec<_>>();
+
+    let mut distances = vec![vec![1; grid[0].len()]; grid.len()];
+
+    let mut empty_col = vec![true; grid[0].len()];
+    for (i, line) in grid.iter().enumerate() {
+        empty_col = empty_col.iter().enumerate().map(|(i, &l)| l && !line[i]).collect();
+        if !line.iter().any(|&x| x) {
+            distances[i] = vec![inflation_arg; line.len()];
+        }
+    }
+
+    for (i, &col) in empty_col.iter().enumerate() {
+        if col {
+            for j in 0..distances.len() {
+                distances[j][i] = inflation_arg;
+            }
+        }
+    }
+
+    let galaxies: Vec<(usize, usize)> = grid.iter().
+        enumerate().
+        map(|(i, line)| line.iter()
+            .enumerate()
+            .filter_map(|(j, &x)| if x { Some((i, j)) } else { None })
+            .collect::<Vec<_>>()
+        ).flatten().collect::<Vec<_>>();
+
+    galaxies.iter().permutations(2).map(|x| {
+        let (x1, y1): (usize, usize) = *x[0];
+        let (x2, y2): (usize, usize) = *x[1];
+        let mut out = 0;
+        let xrange = x1.min(x2)..x1.max(x2);
+        let yrange = if y1 <= y2 { y1..y2 } else { (y2+1)..(y1+1) };
+        for i in xrange { out += distances[i][if x1 <= x2 {y1} else {y2}] }
+        for j in yrange { out += distances[x1.min(x2)][j] }
+        out as u64
+    } ).sum::<u64>() / 2
+}