solve: day 1, part 1

2020/01/input.txt

@@ -0,0 +1,200 @@
+1337
+1906
+2007
+1939
+818
+1556
+2005
+1722
+1484
+1381
+1682
+1253
+1967
+1718
+2002
+1398
+1439
+1689
+1746
+1979
+1985
+1387
+1509
+1566
+1276
+1625
+1853
+882
+1750
+1390
+1731
+1555
+1860
+1675
+1457
+1554
+1506
+1639
+1543
+1849
+1062
+1869
+1769
+1858
+1916
+1504
+1747
+1925
+1275
+1273
+1383
+1816
+1814
+1481
+1649
+1993
+1759
+1949
+1499
+1374
+1613
+1424
+783
+1765
+1576
+1933
+1270
+1844
+1856
+1634
+1261
+1293
+1741
+668
+1573
+1599
+1877
+1474
+1918
+476
+1515
+1029
+202
+1589
+1867
+1503
+1582
+1605
+1557
+587
+1462
+1955
+1806
+1834
+1739
+1343
+1594
+1622
+1972
+1527
+1798
+1719
+1866
+134
+2000
+1992
+1966
+1909
+1340
+1621
+1921
+1256
+1365
+1314
+1748
+1963
+1379
+1627
+1848
+1977
+1917
+1826
+1716
+1631
+1404
+1936
+1677
+1661
+1986
+1997
+1603
+1932
+1780
+1902
+2009
+1257
+1871
+1362
+1662
+1507
+1255
+1539
+1962
+1886
+1513
+1264
+1873
+1700
+807
+1426
+1697
+1698
+1519
+1791
+1240
+1542
+1497
+1761
+1640
+1502
+1770
+1437
+1333
+1805
+1591
+1644
+1420
+1809
+1587
+1421
+1540
+1942
+470
+1940
+1831
+1247
+1632
+1975
+1774
+1919
+1829
+1944
+1553
+1361
+1483
+1995
+1868
+1601
+1552
+1854
+1490
+1855
+1987
+1538
+1389
+1454
+1427
+1686
+1456
+1974

2020/01/main.hs

@@ -1,4 +0,0 @@
-#!/usr/bin/env runghc
-
-main :: IO ()
-main = putStrLn "Hello, Advent of Code 2020!"

2020/01/part1.hs

@@ -0,0 +1,24 @@
+#!/usr/bin/env runghc
+
+import Data.List
+import Data.Maybe
+
+main :: IO ()
+main =
+  do
+    input <- getInput
+
+    let answer = uncurry (*) $ fromJust $ find isSolutionPair $ pairs input
+
+    putStrLn $ show answer
+
+getInput :: IO [Int]
+getInput = fmap (map read . lines) getContents
+
+pairs :: [a] -> [(a, a)]
+pairs [] = []
+pairs [_] = []
+pairs (x:xs) = [(x, y) | y <- xs] ++ pairs xs
+
+isSolutionPair :: (Int, Int) -> Bool
+isSolutionPair (a, b) = a + b == 2020