Implementation day 1

2020/inputs/01.txt

@@ -0,0 +1,200 @@
+1587
+1407
+1717
+1596
+1566
+1752
+1925
+1847
+1716
+1726
+1611
+1628
+1853
+1864
+1831
+1942
+1634
+1964
+1603
+1676
+1256
+1906
+1655
+1790
+1666
+1470
+1540
+1544
+1100
+1447
+1384
+1464
+1651
+1572
+907
+1653
+1265
+1510
+1639
+1818
+376
+1378
+1132
+1750
+1491
+1788
+1882
+1779
+1640
+1586
+1525
+1458
+1994
+1782
+1412
+1033
+1416
+1813
+1520
+1968
+715
+1396
+1745
+1506
+1024
+1798
+1870
+1615
+1957
+1718
+1349
+1983
+1387
+1738
+1588
+1321
+1160
+1907
+1861
+1940
+1475
+2004
+1852
+1760
+1608
+1028
+1820
+1495
+1811
+1737
+1417
+1316
+1087
+1803
+1595
+1346
+1971
+1692
+1678
+1330
+1480
+1097
+1898
+1973
+1567
+1733
+1336
+1381
+1327
+1670
+1436
+1989
+1334
+89
+1862
+1715
+1743
+1967
+1765
+1402
+1729
+1749
+1671
+1196
+1650
+1089
+1814
+1783
+1225
+1823
+1746
+2009
+1886
+1748
+1481
+1739
+1912
+1663
+1668
+1314
+1594
+705
+1449
+1731
+1487
+1648
+1466
+1317
+1979
+1799
+1926
+1703
+1656
+1978
+2005
+1865
+1982
+1951
+1892
+1713
+1744
+1598
+1606
+1583
+1895
+1804
+1430
+1816
+1364
+1575
+1918
+1431
+1812
+1471
+1797
+928
+1934
+1156
+94
+1563
+1909
+1453
+1392
+1427
+1819
+1524
+1695
+1866
+2008
+1413
+1698
+1051
+1707
+1904
+1681
+1541
+1621
+1421
+1809
+1576

2020/samples/01.txt

@@ -0,0 +1,6 @@
+1721
+979
+366
+299
+675
+1456

2020/src/day01.rs

@@ -1,3 +1,4 @@
+use std::collections::HashSet;
 use std::io::Read;
 
 use crate::common::from_lines;
@@ -6,35 +7,61 @@ use crate::Solution;
 #[derive(Default)]
 pub struct Day01;
 
-fn fuel_required(weight: u32) -> u32 {
-    (weight / 3).saturating_sub(2)
-}
-
-fn recursive_fuel(mut weight: u32) -> u32 {
-    let mut required = 0;
-
-    while weight > 0 {
-        weight = fuel_required(weight);
-        required += weight
-    }
-
-    required
-}
-
 impl Solution for Day01 {
     fn part1(&mut self, input: &mut dyn Read) -> String {
-        let weights: Vec<u32> = from_lines(input);
+        let expenses: HashSet<u32> = from_lines(input);
+        let target = 2020;
 
-        let fuel_required: u32 = weights.into_iter().map(fuel_required).sum();
+        for &expense in expenses.iter() {
+            let partner = target - expense;
+            if expenses.contains(&partner) {
+                return (expense * partner).to_string();
+            }
+        }
 
-        fuel_required.to_string()
+        panic!("No solution found!")
     }
 
     fn part2(&mut self, input: &mut dyn Read) -> String {
-        let weights: Vec<u32> = from_lines(input);
+        let expenses: HashSet<u32> = from_lines(input);
+        let target = 2020;
 
-        let fuel_required: u32 = weights.into_iter().map(recursive_fuel).sum();
+        for &e1 in expenses.iter() {
+            for &e2 in expenses.iter() {
+                let c = e1 + e2;
+                if c > target {
+                    continue;
+                }
 
-        fuel_required.to_string()
+                let e3 = target - e1 - e2;
+
+                if expenses.contains(&e3) {
+                    return (e3 * e1 * e2).to_string();
+                }
+            }
+        }
+
+        panic!("No solution found!")
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const SAMPLE: &[u8] = include_bytes!("../samples/01.txt");
+
+    #[test]
+    fn sample_part1() {
+        let mut day = Day01::default();
+        let result = day.part1(&mut SAMPLE.as_ref());
+        assert_eq!("514579", &result);
+    }
+
+    #[test]
+    fn sample_part2() {
+        let mut day = Day01::default();
+        let result = day.part2(&mut SAMPLE.as_ref());
+        assert_eq!("241861950", &result);
     }
 }