2024-05

crates/core/src/year2024/day05.rs

@@ -1,18 +1,90 @@
-use crate::input::Input;
+use crate::common::array_stack::ArrayStack;
+use crate::input::{on_error, Input};
 
-pub const fn solve(_input: &Input) -> Result<u32, String> {
-    Ok(0)
+pub fn solve(input: &Input) -> Result<u32, String> {
+    let mut page_ordering = [0_u128; 100];
+    let mut sum = 0;
+
+    for line in input.text.lines() {
+        if let Some((before, after)) = line.split_once('|') {
+            let before = parse_page(before)?;
+            let after = parse_page(after)?;
+            page_ordering[before as usize] |= 1 << (after as u128);
+        } else if !line.is_empty() {
+            let mut parts = ArrayStack::<100, u8>::new();
+            for part in line.split(',') {
+                let part = part.parse::<u8>().map_err(|_| on_error())?;
+                parts.push(part)?;
+            }
+            let mut valid = true;
+            for (idx, &before) in parts.slice().iter().enumerate() {
+                for &after in parts.slice().iter().skip(idx + 1) {
+                    if page_ordering[before as usize] & (1 << (after as u128)) == 0 {
+                        valid = false;
+                    }
+                }
+            }
+            sum += match (input.is_part_one(), valid) {
+                (true, true) => parts.elements[parts.len() / 2] as u32,
+                (false, false) => {
+                    let l = parts.slice_mut();
+                    l.sort_unstable_by(|&a, &b| {
+                        0.cmp(&(page_ordering[a as usize] & (1 << (b as u128))))
+                    });
+                    l[l.len() / 2] as u32
+                }
+                _ => 0,
+            };
+        }
+    }
+
+    Ok(sum)
+}
+
+fn parse_page(s: &str) -> Result<u8, String> {
+    let n = s.parse::<u8>().map_err(|_| on_error())?;
+    if n >= 100 {
+        return Err(format!("Too big page number: {n}"));
+    }
+    Ok(n)
 }
 
 #[test]
 pub fn tests() {
     use crate::input::{test_part_one_no_allocations, test_part_two_no_allocations};
 
-    let test_input = "";
-    test_part_one_no_allocations!(test_input => 0);
-    test_part_two_no_allocations!(test_input => 0);
+    let test_input = "47|53
+97|13
+97|61
+97|47
+75|29
+61|13
+75|53
+29|13
+97|29
+53|29
+61|53
+97|53
+61|29
+47|13
+75|47
+97|75
+47|61
+75|61
+47|29
+75|13
+53|13
+
+75,47,61,53,29
+97,61,53,29,13
+75,29,13
+75,97,47,61,53
+61,13,29
+97,13,75,29,47";
+    test_part_one_no_allocations!(test_input => 143);
+    test_part_two_no_allocations!(test_input => 123);
 
     let real_input = include_str!("day05_input.txt");
-    test_part_one_no_allocations!(real_input => 0);
-    test_part_two_no_allocations!(real_input => 0);
+    test_part_one_no_allocations!(real_input => 6612);
+    test_part_two_no_allocations!(real_input => 4944);
 }