day 6 part 2

example.txt

@@ -1,33 +1,2 @@
-seeds: 79 14 55 13
+Time:      7  15   30
-
+Distance:  9  40  200
-seed-to-soil map:
-50 98 2
-52 50 48
-
-soil-to-fertilizer map:
-0 15 37
-37 52 2
-39 0 15
-
-fertilizer-to-water map:
-49 53 8
-0 11 42
-42 0 7
-57 7 4
-
-water-to-light map:
-88 18 7
-18 25 70
-
-light-to-temperature map:
-45 77 23
-81 45 19
-68 64 13
-
-temperature-to-humidity map:
-0 69 1
-1 0 69
-
-humidity-to-location map:
-60 56 37
-56 93 4

input.txt

@@ -1,172 +1,2 @@
-seeds: 5844012 110899473 1132285750 58870036 986162929 109080640 3089574276 100113624 2693179996 275745330 2090752257 201704169 502075018 396653347 1540050181 277513792 1921754120 26668991 3836386950 66795009
+Time:        44     82     69     81
-
+Distance:   202   1076   1138   1458
-seed-to-soil map:
-3547471595 1239929038 174680800
-3052451552 758183681 481745357
-0 1427884524 1775655006
-2844087171 549819300 208364381
-3767989253 4004864866 5194940
-3534196909 1414609838 13274686
-1775655006 114264781 435554519
-4148908402 4010059806 146058894
-2729822390 0 114264781
-3773184193 4156118700 138848596
-2211209525 3203539530 518612865
-3912032789 3767989253 236875613
-
-soil-to-fertilizer map:
-912405184 1056091028 152837752
-194471272 1208928780 200072008
-136115250 240819204 58356022
-3502815281 3536983174 299994001
-2321814552 2458149869 18748048
-3173949445 2623931701 9591555
-394543280 888648379 167442649
-1990258415 3891640206 212931291
-1068754270 54862533 153774684
-1222528954 660792432 186471834
-3340878967 3405750148 131233026
-3472111993 3836977175 30703288
-561985929 299175226 225501956
-2942828492 4104571497 88527954
-874532405 850775600 37872779
-3031356446 3867680463 23959743
-842350418 208637217 32181987
-0 524677182 136115250
-1065242936 847264266 3511334
-2203189706 2339525023 118624846
-1929736108 2563409394 60522307
-3802809282 1847367009 492158014
-1847367009 2790861223 82369099
-2442430445 2873230322 500398047
-3183541000 2633523256 157337967
-3141827666 3373628369 32121779
-787487885 0 54862533
-3055316189 2476897917 86511477
-2340562600 4193099451 101867845
-
-fertilizer-to-water map:
-798315344 439687669 1930292
-1174979421 2966258900 475289790
-439687669 778614573 55925503
-3743699694 3453541232 155280637
-2989334775 1659556189 96021468
-1650269211 3441548690 11992542
-3898980331 3608821869 395986965
-1705125292 2123762646 842496254
-3375514705 1755577657 368184989
-646363825 441617961 94777173
-1662261753 1616692650 42863539
-495613172 627863920 150750653
-2777061135 1174979421 212273640
-741140998 834540076 57174346
-800245636 536395134 91468786
-2547621546 1387253061 229439589
-3085356243 4004808834 290158462
-
-water-to-light map:
-541719462 212840988 165903288
-3437755571 1615831015 672632835
-1051033542 2678450187 510773217
-243353905 378744276 104057369
-1561806759 3801474127 134575711
-707622750 677109833 258560892
-2580483557 1051033542 195631857
-0 935670725 30512917
-347411274 482801645 194308188
-30512917 0 127836567
-2190497220 2288463850 389986337
-3068589955 1246665399 369165616
-1754579039 3936049838 66442917
-4110388406 3616895237 184578890
-158349484 127836567 85004421
-2776115414 4002492755 292474541
-1821021956 3247419973 369475264
-1696382470 3189223404 58196569
-
-light-to-temperature map:
-338228166 2812162941 77503977
-3123877206 693964345 40932068
-3939438903 614787731 633466
-3301169239 2299402886 215156012
-3516325251 499164007 115623724
-3852145506 3365439095 87293397
-875755064 3565078024 729889272
-2849390436 734896413 11914872
-2861305308 215265512 77518872
-4220385528 2056242491 68417151
-2221674563 3167682469 34693717
-2765973467 292784384 83416969
-3198884011 1699097031 22283517
-3164809274 2889666918 34074737
-809366712 746811285 52314986
-4096970661 1633036395 58945085
-3221167528 2699611924 80001711
-697021180 3452732492 112345532
-2059345064 799126271 162329499
-4155915746 629494563 64469782
-2431111524 1721380548 334861943
-684283267 2779613635 12737913
-440342453 2923741655 243940814
-3634265609 961455770 217879897
-4288802679 3202376186 6164617
-415732143 1691981480 4798917
-1605644336 1179335667 453700728
-420531060 2792351548 19811393
-3631948975 1696780397 2316634
-2938824180 2514558898 185053026
-215265512 376201353 122962654
-2256368280 2124659642 174743244
-3940072369 3208540803 156898292
-861681698 615421197 14073366
-
-temperature-to-humidity map:
-841576398 2731200418 60836938
-1860695540 395011682 292982985
-1518037021 3432774193 53954373
-1786573987 2461900019 55353430
-2940303448 1995108352 6974538
-3014069287 1664464874 53916789
-753139746 2190061656 88436652
-2351822957 2925825589 209990361
-3079884326 3498626816 37609115
-4067060121 4186346579 108620717
-4175680838 4102322798 3778367
-1571991394 2415899186 46000833
-2841627583 1157034722 22534242
-1841927417 2517253449 18768123
-2153678525 47765849 108568164
-3251281674 1179568964 226737882
-3067986076 3486728566 11898250
-1308101633 1785172964 209935388
-2262246689 1406306846 89576268
-902413336 2278498308 137400878
-1039814214 3765380846 268287419
-45422022 156334013 238677669
-3617672799 2612163195 119037223
-2947277986 1718381663 66791301
-1617992227 1495883114 168581760
-284099691 687994667 469040055
-4214721882 4106101165 80245414
-2839283756 45422022 2343827
-3117493441 2792037356 133788233
-2864161825 2536021572 76141623
-4179459205 4067060121 35262677
-3736710022 3135815950 296958243
-3478019556 2002082890 139653243
-2610138841 3536235931 229144915
-2561813318 2141736133 48325523
-
-humidity-to-location map:
-608325534 0 231346900
-222429954 453776854 385895580
-3710263359 3540956206 563631409
-1193511298 1116937854 38719102
-1702450793 1176729484 153572024
-1694669826 1109156887 7780967
-0 231346900 222429954
-1856022817 1686715664 1854240542
-1588644556 4104587615 106025270
-1109156887 4210612885 84354411
-4273894768 1155656956 21072528
-1232230400 1330301508 356414156

src/main.rs

@@ -1,242 +1,76 @@
-use std::cmp::{max, min};
+use std::io::stdin;
-use std::{collections::HashMap, io::stdin};
 
-use anyhow::Result;
+use anyhow::{bail, Result};
 use regex::Regex;
 
-#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+/// solve ax² + bx + c = 0
-struct Range {
+fn solve_quadratic(a: f64, b: f64, c: f64) -> (f64, f64) {
-    start: i64,
+    let r1 = (-b + f64::sqrt(b * b - 4.0 * a * c)) / 2.0 * a;
-    len: i64,
+    let r2 = (-b - f64::sqrt(b * b - 4.0 * a * c)) / 2.0 * a;
+    (r1, r2)
 }
 
-impl Range {
+fn parse_input() -> Result<(Vec<i64>, Vec<i64>)> {
-    fn intersection(&self, other: &Range) -> Option<Range> {
-        let i1 = max(self.start, other.start);
-        let i2 = min(self.start + self.len, other.start + other.len);
-
-        if i1 >= i2 {
-            return None;
-        }
-
-        Some(Range {
-            start: i1,
-            len: i2 - i1,
-        })
-    }
-}
-
-#[derive(Debug, Clone, Copy)]
-struct RangeMap {
-    from: i64,
-    to: i64,
-    len: i64,
-}
-
-#[derive(Debug)]
-struct SeedsMap {
-    range_maps: Vec<RangeMap>,
-}
-
-impl SeedsMap {
-    fn new() -> SeedsMap {
-        SeedsMap { range_maps: vec![] }
-    }
-
-    fn add_range(&mut self, range: (i64, i64, i64)) {
-        self.range_maps.push(RangeMap {
-            from: range.1,
-            to: range.0,
-            len: range.2,
-        });
-        self.range_maps.sort_by_key(|r| r.from);
-    }
-
-    fn map(&self, ranges: &[Range]) -> Vec<Range> {
-        let mut result = vec![];
-        for r in ranges {
-            result.extend(self.map_single_range(r));
-        }
-        result
-    }
-
-    fn map_single_range(&self, range: &Range) -> Vec<Range> {
-        if self.range_maps.is_empty() {
-            return vec![*range];
-        }
-
-        let mut result = vec![];
-        let first = self.range_maps.first().unwrap();
-        let last = self.range_maps.last().unwrap();
-        let left = min(range.start, first.from);
-        let right = max(range.start + range.len, last.from + last.len);
-
-        let mut last = left;
-        for rm in &self.range_maps {
-            // first, a range from last to rm.start, with no mapping
-            let r = Range {
-                start: last,
-                len: rm.from - last,
-            };
-            if let Some(i) = r.intersection(range) {
-                result.push(i);
-            }
-            // second, a range from rm.start, with mapping
-            let r = Range {
-                start: rm.from,
-                len: rm.len,
-            };
-            if let Some(i) = r.intersection(range) {
-                result.push(Range {
-                    start: rm.to + i.start - rm.from,
-                    len: i.len,
-                });
-                last = i.start + i.len;
-            }
-        }
-
-        let r = Range {
-            start: last,
-            len: right - last,
-        };
-        if let Some(i) = r.intersection(range) {
-            result.push(i);
-        }
-
-        result
-    }
-}
-
-fn parse_input(seed_ranges: &mut Vec<Range>, maps: &mut HashMap<String, SeedsMap>) -> Result<()> {
     let numbers = Regex::new(r"(\d+)")?;
-    let pairs = Regex::new(r"(\d+) (\d+)")?;
+    let mut times = vec![];
-    let mut current_map = String::new();
+    let mut distances = vec![];
     for line in stdin().lines().map_while(Result::ok) {
-        if line.starts_with("seeds:") {
+        if line.starts_with("Time:") {
-            *seed_ranges = pairs
+            times = numbers
-                .captures_iter(&line)
+                .captures_iter(&line.replace(' ', ""))
-                .map(|c| -> Result<Range> {
-                    Ok(Range {
-                        start: c.get(1).unwrap().as_str().parse()?,
-                        len: c.get(2).unwrap().as_str().parse()?,
-                    })
-                })
-                .map_while(Result::ok)
-                .collect();
-        } else if line.ends_with(" map:") {
-            current_map = line
-                .split_whitespace()
-                .next()
-                .unwrap_or_default()
-                .to_owned();
-        } else {
-            let nums: Vec<i64> = numbers
-                .captures_iter(&line)
                 .map(|c| c.get(1).unwrap().as_str().parse())
                 .map_while(Result::ok)
                 .collect();
-            if nums.len() == 3 {
+        } else if line.starts_with("Distance:") {
-                let map = maps
+            distances = numbers
-                    .entry(current_map.clone())
+                .captures_iter(&line.replace(' ', ""))
-                    .or_insert_with(SeedsMap::new);
+                .map(|c| c.get(1).unwrap().as_str().parse())
-                map.add_range((nums[0], nums[1], nums[2]));
+                .map_while(Result::ok)
-            }
+                .collect();
+        } else {
+            bail!("unexpected line: {}", line);
         }
     }
-    Ok(())
+    Ok((times, distances))
 }
 
 fn main() -> Result<()> {
-    let mut maps: HashMap<String, SeedsMap> = HashMap::new();
+    let (times, distances) = parse_input()?;
-    let mut seed_ranges: Vec<Range> = vec![];
 
-    parse_input(&mut seed_ranges, &mut maps)?;
+    if times.len() != distances.len() {
-
+        bail!(
-    let map_names = [
+            "times has {} elements, but distances has {} elements",
-        "seed-to-soil",
+            times.len(),
-        "soil-to-fertilizer",
+            distances.len()
-        "fertilizer-to-water",
+        );
-        "water-to-light",
-        "light-to-temperature",
-        "temperature-to-humidity",
-        "humidity-to-location",
-    ];
-
-    let mut locations = vec![];
-    for range in seed_ranges {
-        let mut mapped_ranges = vec![range];
-        for map_name in map_names {
-            let mapped = maps.get(map_name).unwrap().map(&mapped_ranges);
-            mapped_ranges = mapped;
-        }
-        locations.extend(mapped_ranges.iter().map(|r| r.start));
     }
-    println!("{}", locations.iter().min().unwrap());
+
+    let mut prod = 1;
+    for i in 0..times.len() {
+        let t = times[i];
+        let d = distances[i];
+
+        // the equation to solve is x * (t - x) - d = 0
+        //  = t*x - x*x - d = 0
+        //  = -1x² + tx - d = 0
+        let (r1, r2) = solve_quadratic(-1.0, t as f64, -d as f64);
+        let r1 = (r1 + 1.0).floor() as i64;
+        let r2 = (r2 - 1.0).ceil() as i64;
+
+        let ways = (r2 - r1) + 1;
+
+        println!("{t} {d}");
+        println!("ways: {ways}");
+        prod *= ways;
+    }
+
+    println!("{prod}");
     Ok(())
 }
 
 #[cfg(test)]
 mod tests {
-    use super::*;
 
     #[test]
-    fn test_intersections() {
+    fn test() {}
-        let l = |r1: &Range, r2: &Range| r1.intersection(r2);
-        assert_eq!(
-            l(&Range { start: 1, len: 3 }, &Range { start: 1, len: 3 }),
-            Some(Range { start: 1, len: 3 })
-        );
-        assert_eq!(
-            l(&Range { start: 1, len: 2 }, &Range { start: 1, len: 3 }),
-            Some(Range { start: 1, len: 2 })
-        );
-        assert_eq!(
-            l(&Range { start: 2, len: 4 }, &Range { start: 0, len: 3 }),
-            Some(Range { start: 2, len: 1 })
-        );
-        assert_eq!(
-            l(&Range { start: 0, len: 3 }, &Range { start: 2, len: 4 }),
-            Some(Range { start: 2, len: 1 })
-        );
-        assert_eq!(
-            l(&Range { start: 3, len: 4 }, &Range { start: 0, len: 3 }),
-            None
-        );
-        assert_eq!(
-            l(&Range { start: 0, len: 10 }, &Range { start: 4, len: 4 }),
-            Some(Range { start: 4, len: 4 })
-        );
-    }
-
-    #[test]
-    fn test_range_map() {
-        let mut m = SeedsMap::new();
-        m.add_range((52, 50, 48));
-        m.add_range((50, 98, 2));
-        let r = m.map_single_range(&Range { start: 79, len: 14 });
-        assert_eq!(r, [Range { start: 81, len: 14 }]);
-
-        let mut m = SeedsMap::new();
-        m.add_range((39, 0, 15));
-        m.add_range((0, 15, 37));
-        m.add_range((37, 52, 2));
-        let r = m.map_single_range(&Range { start: 81, len: 14 });
-        assert_eq!(r, [Range { start: 81, len: 14 }]);
-
-        let mut m = SeedsMap::new();
-        m.add_range((88, 18, 7));
-        m.add_range((18, 25, 70));
-        let r = m.map_single_range(&Range { start: 81, len: 14 });
-        assert_eq!(r, [Range { start: 74, len: 14 }]);
-
-        let mut m = SeedsMap::new();
-        m.add_range((81, 45, 19));
-        m.add_range((68, 64, 13));
-        m.add_range((45, 77, 23));
-        let r = m.map_single_range(&Range { start: 74, len: 14 });
-        assert_eq!(
-            r,
-            [Range { start: 78, len: 3 }, Range { start: 45, len: 11 }]
-        );
-    }
 }