add day11 part 1

day11/stones.go

@@ -0,0 +1,76 @@
+package main
+
+import (
+    "os"
+    "fmt"
+    "strconv"
+    "strings"
+)
+
+
+// general util
+func check(e error) {
+    if e != nil { panic(e) }
+}
+
+func apply_rules(arr []int) []int {
+    for i, e := range arr {
+        switch {
+            // rule 1
+            case e == 0:
+                arr[i] = 1
+            // mark for rule 2
+            case len(strconv.Itoa(e)) % 2 == 0:
+                arr[i] = -e
+            // rule 3
+            default:
+                arr[i] = e * 2024
+        }
+    }
+    // rule 2
+    arr_cp := make([]int, len(arr))
+    copy(arr_cp, arr)
+    arr = arr[:0]
+
+    for _, e := range arr_cp {
+        if e > 0 {
+            arr = append(arr, e)
+        } else {
+            e_str := strconv.Itoa(-e)
+            num1, err := strconv.Atoi(e_str[:len(e_str) / 2])
+            check(err)
+            num2, err := strconv.Atoi(e_str[len(e_str) / 2:])
+            check(err)
+            
+            arr = append(arr, num1)
+            arr = append(arr, num2)
+        }
+    }
+
+    return arr
+}
+
+
+// main loop
+func main() {
+
+    // read in file
+    dat, err := os.ReadFile("data.txt")
+    check(err)
+    dat_str := strings.TrimSpace(string(dat))
+    line_arr := strings.Split(dat_str, " ")
+
+    // convert to list of numbers
+    numbers := make([]int, 0, len(line_arr))
+
+    for _, e := range line_arr {
+        num, err := strconv.Atoi(e)
+        check(err)
+        numbers = append(numbers, num)
+    }
+
+    for range 75 {
+        numbers = apply_rules(numbers)
+    }
+    fmt.Println(len(numbers))
+}