add day3

day3/mul.go

@@ -0,0 +1,36 @@
+package main
+
+import (
+    "fmt"
+    "os"
+    "regexp"
+    "strconv"
+)
+
+func check(e error) {
+    if e != nil { panic(e) }
+}
+
+func main() {
+
+    dat, err := os.ReadFile("data.txt")
+    check(err)
+    dat_str := string(dat)
+    
+    // get all numbers within mul(*,*) using capture groups
+    r := regexp.MustCompile("mul\\(([0-9]{1,3}),([0-9]{1,3})\\)")
+    matches := r.FindAllStringSubmatch(dat_str, -1)
+    
+    acc := 0
+    for _, elem := range matches {
+        // convert to numbers
+        num1, err := strconv.Atoi(elem[1])
+        check(err)
+        num2, err := strconv.Atoi(elem[2])
+        check(err)
+
+        acc += num1 * num2
+    }
+
+    fmt.Println(acc)
+}