go: add mod

2020/day01/go.mod

@@ -0,0 +1,3 @@
+module 2020/day01
+
+go 1.25.4

2020/day01/input.txt

@@ -0,0 +1,200 @@
+2004
+1671
+1678
+1304
+1242
+1882
+1605
+1034
+1883
+1589
+1881
+1546
+1713
+1218
+1982
+1395
+1277
+1417
+1497
+1499
+1847
+1989
+1172
+1684
+1243
+1843
+1661
+1662
+1421
+1790
+1344
+1458
+1074
+1809
+1990
+1369
+1386
+1736
+1972
+1634
+1229
+1123
+1870
+1595
+1934
+1399
+1732
+1545
+1208
+368
+1907
+1143
+443
+1929
+1965
+1872
+1738
+1967
+997
+1473
+1041
+1991
+1868
+1180
+1409
+1379
+1568
+1163
+1869
+1391
+1956
+1249
+1505
+351
+2001
+462
+1219
+1731
+1802
+1798
+1626
+1438
+1099
+1477
+1980
+1708
+1666
+1066
+1121
+1359
+1426
+1734
+1768
+1836
+1453
+923
+1660
+1878
+1522
+1024
+1429
+232
+1952
+1730
+1763
+1981
+1388
+1337
+1317
+1922
+1044
+1999
+1341
+1178
+1524
+1185
+1257
+1256
+1061
+1262
+1022
+1778
+1917
+1205
+1272
+1842
+1533
+1194
+1746
+1691
+1617
+1667
+1940
+1171
+1792
+1773
+1411
+1902
+1859
+1978
+1764
+1482
+1276
+735
+1716
+1915
+1675
+1126
+1830
+1227
+1299
+1535
+1700
+1658
+1771
+1823
+1055
+1602
+1590
+1983
+1885
+1735
+103
+1766
+14
+1486
+1939
+1525
+1916
+1279
+544
+1406
+1674
+1948
+1971
+1651
+1715
+1943
+1784
+2008
+1800
+1720
+1557
+1467
+1371
+1637
+1345
+1924
+1565
+1976
+1827
+1890
+1848
+1465
+1573
+1231
+1310
+1754
+1569
+1532

2020/day01/main.go

@@ -0,0 +1,58 @@
+package main
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"strconv"
+	"strings"
+)
+
+func parseInput(file string) []int {
+	content, err := os.ReadFile(file)
+	if err != nil {
+		log.Fatalf("Failed to read input file: %v", err)
+	}
+	lines := strings.Fields(string(content))
+	var data []int
+	for _, line := range lines {
+		num, err := strconv.Atoi(line)
+		if err != nil {
+			log.Fatalf("Failed to convert string to int: %v", err)
+		}
+		data = append(data, num)
+	}
+	return data
+}
+
+func PartOne(data []int) int {
+	seen := make(map[int]bool)
+	for _, number := range data {
+		complement := 2020 - number
+		if seen[complement] {
+			return number * complement
+		}
+		seen[number] = true
+	}
+	return 0
+}
+
+func PartTwo(data []int) int {
+	seen := make(map[int]bool)
+	for idx := range data {
+		for _, number := range data[idx+1:] {
+			complement := 2020 - data[idx] - number
+			if seen[complement] {
+				return complement * data[idx] * number
+			}
+		}
+		seen[data[idx]] = true
+	}
+	return 0
+}
+
+func main() {
+	data := parseInput("input.txt")
+	fmt.Println("Part 1:", PartOne(data))
+	fmt.Println("Part 2:", PartTwo(data))
+}

2020/day01/main_test.go

@@ -0,0 +1,21 @@
+package main
+
+import "testing"
+
+func TestPartOne(t *testing.T) {
+	input := []int{1721, 979, 366, 299, 675, 1456}
+	expected := 514579
+	got := PartOne(input)
+	if got != expected {
+		t.Errorf("PartOne(%v) = %d, want %d", input, got, expected)
+	}
+}
+
+func TestPartTwo(t *testing.T) {
+	input := []int{1721, 979, 366, 299, 675, 1456}
+	expected := 241861950
+	got := PartTwo(input)
+	if got != expected {
+		t.Errorf("PartTwo(%v) = %d, want %d", input, got, expected)
+	}
+}