2022 day 8 part 2 interim

2022/rust/src/solutions/day08.rs

@@ -1,3 +1,5 @@
+use std::cmp::max;
+use std::collections::HashMap;
 use crate::utils;
 
 
@@ -31,11 +33,7 @@ fn create_mask(data: &[Vec<i32>]) -> Vec<Vec<bool>> {
 
     let mut visible: Vec<Vec<bool>> = (0..rows)
         .into_iter()
-        .map(|_| (0..cols)
-            .into_iter()
-            .map(|_| false)
-            .collect()
-        )
+        .map(|_| (0..cols).into_iter().map(|_| false).collect())
         .collect();
 
     for row in 0..rows {
@@ -63,18 +61,74 @@ fn create_mask(data: &[Vec<i32>]) -> Vec<Vec<bool>> {
 
 
 fn solve1(data: &[Vec<i32>]) -> usize {
-    let mask = create_mask(data);
+    create_mask(data).into_iter().map(|row| row.iter().filter(|&e| *e).count()).sum()
+}
 
-    mask.into_iter()
-        .map(|row| row.iter()
-            .filter(|&e| *e)
-            .count()
-        )
-        .sum()
+#[inline(always)]
+fn find_limit(
+    data: &[Vec<i32>],
+    last_heights: &mut HashMap<i32, usize>,
+    row: usize,
+    col: usize
+) -> usize {
+    let mut limit = 0;
+    for h in data[row][col]..=9 {
+        if let Some(since) = last_heights.get(&h) {
+            limit = max(limit, *since);
+        }
+    };
+    limit
+}
+
+fn find_scores(data: &[Vec<i32>]) -> Vec<Vec<i32>> {
+    let rows = data.len();
+    let cols = data[0].len();
+
+    let mut scores: Vec<Vec<i32>> = (0..rows)
+        .into_iter()
+        .map(|_| (0..cols).into_iter().map(|_| 1).collect())
+        .collect();
+
+    for row in 0..rows {
+        let mut last_heights: HashMap<i32, usize> = HashMap::new();
+        for col in 0..cols {
+            let limit = find_limit(data, &mut last_heights, row, col);
+            scores[row][col] = scores[row][col] * (col - limit) as i32;
+            last_heights.insert(data[row][col], col);
+        };
+        let mut last_heights: HashMap<i32, usize> = HashMap::new();
+        for col in (0..cols).rev() {
+            let limit = find_limit(data, &mut last_heights, row, col);
+            let limit = if limit == 0 { cols - 1 } else { limit };
+            scores[row][col] = scores[row][col] * (limit - col) as i32;
+            last_heights.insert(data[row][col], col);
+        };
+    };
+
+    for col in 0..cols {
+        let mut last_heights: HashMap<i32, usize> = HashMap::new();
+        for row in 0..rows {
+            let limit = find_limit(data, &mut last_heights, row, col);
+            scores[row][col] = scores[row][col] * (row - limit) as i32;
+            last_heights.insert(data[row][col], row);
+        };
+        let mut last_heights: HashMap<i32, usize> = HashMap::new();
+        for row in (0..cols).rev() {
+            let limit = find_limit(data, &mut last_heights, row, col);
+            let limit = if limit == 0 { rows - 1 } else { limit };
+            scores[row][col] = scores[row][col] * (limit - row) as i32;
+            last_heights.insert(data[row][col], row);
+        };
+    };
+
+    scores
 }
 
 fn solve2(data: &[Vec<i32>]) -> i32 {
-    2
+    let scores = find_scores(data);
+
+    let reducer = |a, b| max(a, b);
+    scores.into_iter().map(|row| row.iter().copied().reduce(reducer).unwrap()).reduce(reducer).unwrap()
 }
 
 
@@ -110,6 +164,9 @@ mod tests {
     #[test]
     fn part2() {
         let data = parse_data(DATA);
-        assert_eq!(2, solve2(&data));
+        let scores = find_scores(&data);
+        assert_eq!(4, scores[1][2]);
+        assert_eq!(8, scores[3][2]);
+        assert_eq!(8, solve2(&data));
     }
 }