feat(2025): add day2

2025/day2/day2.go

@@ -0,0 +1,87 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+)
+
+func isInvalid(num int) bool {
+	s := strconv.Itoa(num)
+	n := len(s)
+	if n%2 != 0 || n < 2 {
+		return false
+	}
+	half := n / 2
+	return s[:half] == s[half:]
+}
+
+func part1() {
+	data, _ := os.ReadFile("input.txt")
+	content := strings.TrimSpace(string(data))
+	ranges := strings.Split(content, ",")
+	sum := 0
+	for _, v := range ranges {
+		arr := strings.Split(v, "-")
+		start, _ := strconv.Atoi(arr[0])
+		end, _ := strconv.Atoi(arr[1])
+		for i := start; i <= end; i++ {
+			if isInvalid(i) {
+				// fmt.Printf("%d\n", i)
+				sum += i
+			}
+		}
+	}
+	fmt.Printf("%d\n", sum)
+}
+
+func isRepeating(num int) bool {
+	s := strconv.Itoa(num)
+	n := len(s)
+	if n <= 1 {
+		return false
+	}
+
+	for k := 1; k <= n/2; k++ {
+		if n%k != 0 {
+			continue
+		}
+
+		isRepeat := true
+		for i := k; i < n; i++ {
+			if s[i] != s[i%k] {
+				isRepeat = false
+				break
+			}
+		}
+		if isRepeat {
+			return true
+		}
+	}
+	return false
+}
+
+func part2() {
+	data, _ := os.ReadFile("input.txt")
+	content := strings.TrimSpace(string(data))
+	ranges := strings.Split(content, ",")
+	sum := 0
+	for _, v := range ranges {
+		arr := strings.Split(v, "-")
+		start, _ := strconv.Atoi(arr[0])
+		end, _ := strconv.Atoi(arr[1])
+		for i := start; i <= end; i++ {
+			if isRepeating(i) {
+				// fmt.Printf("%d\n", i)
+				sum += i
+			}
+		}
+	}
+	fmt.Printf("%d\n", sum)
+}
+
+func main() {
+	part1()
+	part2()
+}

2025/day2/go.mod

@@ -0,0 +1,3 @@
+module day2
+
+go 1.23.4