complete day 8 part 1

src/main.rs

@@ -1,41 +1,27 @@
-use std::cmp;
+use std::collections::HashMap;
 use std::fs::File;
 use std::io::{BufRead, BufReader};
 use std::str;
 
-fn process_lines(mut reader: impl BufRead) -> anyhow::Result<usize> {
-    let mut line = String::new();
-    reader.read_to_string(&mut line)?;
-    let initial_state = line
-        .trim()
-        .split(',')
-        .map(|token| token.trim().parse::<u32>())
-        .collect::<Result<Vec<u32>, _>>()?;
-    let pos_offset = *initial_state.iter().min().unwrap();
-    let pos_max = ((*initial_state.iter().max().unwrap()) - pos_offset) as usize;
-    let mut histogram = vec![0u32; pos_max + 1];
-    initial_state.into_iter().for_each(|i| {
-        histogram[(i - pos_offset) as usize] += 1;
-    });
-
-    (0..=pos_max)
-        .map(|pos| {
-            histogram
-                .iter()
-                .copied()
-                .enumerate()
-                .map(|(i, count)| {
-                    // gas(n) = summa [i = 0 -> n]{n - i}
-                    //        = summa [i = 0 -> n]{i}
-                    //        = n*(n+1)/2
-                    let distance = cmp::max(i, pos) - cmp::min(i, pos);
-                    let individual_use = distance * (distance + 1) / 2;
-                    (count as usize) * individual_use
-                })
-                .sum()
-        })
-        .min()
-        .ok_or_else(|| unreachable!())
+fn process_lines(reader: impl BufRead) -> anyhow::Result<usize> {
+    let mut digit_count: HashMap<usize, usize> = HashMap::with_capacity(4);
+    digit_count.insert(2, 0);
+    digit_count.insert(3, 0);
+    digit_count.insert(4, 0);
+    digit_count.insert(7, 0);
+    for line_res in reader.lines() {
+        let line = line_res?;
+        line.split('|')
+            .next_back()
+            .map(|s| s.trim())
+            .expect("malformed input")
+            .split_whitespace()
+            .map(|digit| digit.chars().count())
+            .for_each(|count| {
+                digit_count.entry(count).and_modify(|v| *v += 1);
+            });
+    }
+    Ok(digit_count.into_values().sum())
 }
 fn main() {
     const INPUT_PATH: &str = "data/input.txt";
@@ -45,8 +31,8 @@ fn main() {
             Err(err) => {
                 eprintln!("Could not process file {}:\n  {}", INPUT_PATH, err);
             }
-            Ok(gas_use) => {
-                println!("min gas use: {}", gas_use);
+            Ok(digit_count) => {
+                println!("# special digits: {}", digit_count);
             }
         },
         Err(err) => {