From 3e9ff4ded0c36462c34816fab0b047f3ef6ee34c Mon Sep 17 00:00:00 2001
From: Noratrieb <48135649+Noratrieb@users.noreply.github.com>
Date: Sat, 7 Dec 2024 14:50:59 +0100
Subject: [PATCH] optimize d7p2

---
 2024/day07/src/lib.rs | 79 ++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 78 insertions(+), 1 deletion(-)

diff --git a/2024/day07/src/lib.rs b/2024/day07/src/lib.rs
index d39776b..4e68e85 100644
--- a/2024/day07/src/lib.rs
+++ b/2024/day07/src/lib.rs
@@ -14,6 +14,8 @@ helper::define_variants! {
     part2 {
         basic => crate::part2,sample_count=500;
         no_string_fmt => crate::part2_no_string_fmt,sample_count=1000;
+        order => crate::part2_order,sample_count=1000;
+        parsing => crate::part2_parsing,sample_count=5000;
     }
 }
 
@@ -127,6 +129,81 @@ fn part2_no_string_fmt(input: &str) -> u64 {
     total
 }
 
+fn part2_order(input: &str) -> u64 {
+    let mut total = 0;
+    for line in input.lines() {
+        let (result, values) = line.split_once(": ").unwrap();
+        let result = parse_unwrap(result);
+        let values = values
+            .split(" ")
+            .map(|val| (val, parse_unwrap(val)))
+            .collect::<Vec<_>>();
+
+        fn does_work(values: &[(&str, u64)], result: u64) -> bool {
+            if values.len() == 1 {
+                return values[0].1 == result;
+            }
+
+            let (l_str, l) = *values.last().unwrap();
+            let next = &values[..(values.len() - 1)];
+            let thousand = 10_u64.pow(l_str.len() as u32);
+
+            let concat_works = result % thousand == l;
+            let mul_works = result % l == 0;
+            let sub_works = l <= result;
+
+            // Concat is the least common, so doing it first helps remove the most possibilities.
+            false
+                || (concat_works && does_work(next, result / thousand))
+                || (mul_works && does_work(next, result / l))
+                || (sub_works && does_work(next, result - l))
+        }
+
+        if does_work(&values, result) {
+            total += result;
+        }
+    }
+    total
+}
+
+fn part2_parsing(input: &str) -> u64 {
+    let mut total = 0;
+
+    let mut values = Vec::new();
+
+    for line in input.lines() {
+        values.clear();
+        let (result, values_str) = line.split_once(": ").unwrap();
+        let result = parse_unwrap(result);
+        values.extend(values_str.split(' ').map(|val| (val, parse_unwrap(val))));
+
+        fn does_work(values: &[(&str, u64)], result: u64) -> bool {
+            if values.len() == 1 {
+                return values[0].1 == result;
+            }
+
+            let (l_str, l) = *values.last().unwrap();
+            let next = &values[..(values.len() - 1)];
+            let thousand = 10_u64.pow(l_str.len() as u32);
+
+            let concat_works = result % thousand == l;
+            let mul_works = result % l == 0;
+            let sub_works = l <= result;
+
+            // Concat is the least common, so doing it first helps remove the most possibilities.
+            false
+                || (concat_works && does_work(next, result / thousand))
+                || (mul_works && does_work(next, result / l))
+                || (sub_works && does_work(next, result - l))
+        }
+
+        if does_work(&values, result) {
+            total += result;
+        }
+    }
+    total
+}
+
 helper::tests! {
     day07 Day07;
     part1 {
@@ -135,7 +212,7 @@ helper::tests! {
     }
     part2 {
         small => 11387;
-        default => 0;
+        default => 146111650210682;
     }
 }
 helper::benchmarks! {}