Solve day three

.gitignore

@@ -0,0 +1 @@
+*.txt

three.go

@@ -1,95 +0,0 @@
-package main
-
-import (
-	"bufio"
-	"fmt"
-	"os"
-	"strconv"
-	"strings"
-)
-
-func check(e error) {
-	if e != nil {
-		panic(e)
-	}
-}
-
-func is_safe(levels []int) bool {
-	all_diffs_neg := true
-	all_diffs_pos := true
-
-	prev := levels[0]
-	for i, level := range levels {
-		if i == 0 {
-			prev = level
-			continue
-		}
-
-		diff := level - prev
-		if diff > 3 || diff < -3 || diff == 0 {
-			return false
-		}
-
-		all_diffs_pos = all_diffs_pos && diff > 0
-		all_diffs_neg = all_diffs_neg && diff < 0
-		prev = level
-	}
-
-	return all_diffs_neg || all_diffs_pos
-}
-
-func is_safe_with_dampener(levels []int) bool {
-	if is_safe(levels) {
-		return true
-	}
-
-	for i := range levels {
-		damped_levels := make([]int, 0, len(levels)-1)
-		for j, val := range levels {
-			if i == j {
-				continue
-			}
-
-			damped_levels = append(damped_levels, val)
-		}
-
-		if is_safe(damped_levels) {
-			return true
-		}
-	}
-
-	return false
-}
-
-func main() {
-	f, err := os.Open("./two.txt")
-	defer f.Close()
-	check(err)
-
-	n_safe := 0
-	n_dampener_safe := 0
-
-	scanner := bufio.NewScanner(f)
-	for scanner.Scan() {
-
-		line := scanner.Text()
-		fields := strings.Fields(line)
-
-		levels := make([]int, 0, 5)
-
-		for _, field := range fields {
-			level, err := strconv.Atoi(field)
-			check(err)
-			levels = append(levels, level)
-		}
-		if is_safe(levels) {
-			n_safe += 1
-		}
-		if is_safe_with_dampener(levels) {
-			n_dampener_safe += 1
-		}
-	}
-
-	fmt.Println(n_safe)
-	fmt.Println(n_dampener_safe)
-}

three/three.go

@@ -0,0 +1,88 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"regexp"
+	"strconv"
+)
+
+var mul_re *regexp.Regexp = regexp.MustCompile(`mul\(([0-9]+),([0-9]+)\)`)
+
+func check(e error) {
+	if e != nil {
+		panic(e)
+	}
+}
+
+func handle_muls(input string) int {
+	total := 0
+
+	matches := mul_re.FindAllStringSubmatch(input, -1)
+	for _, match := range matches {
+		first, err := strconv.Atoi(match[1])
+		check(err)
+		second, err := strconv.Atoi(match[2])
+		check(err)
+
+		total += first * second
+	}
+	return total
+}
+
+func next(matches [][]int, start int) [][]int {
+	for i, match := range matches {
+		if match[0] > start {
+			return matches[i:]
+		}
+	}
+	return nil
+}
+
+func main() {
+	instructions, err := os.ReadFile("./three.txt")
+	check(err)
+
+	str_instructions := string(instructions)
+
+	// Find all mul instructions
+	fmt.Println(handle_muls(str_instructions))
+
+	// Handle disables and enables
+	total := 0
+	enable_re := regexp.MustCompile(`do\(\)`)
+	disable_re := regexp.MustCompile(`don't\(\)`)
+	dos := enable_re.FindAllStringIndex(str_instructions, -1)
+	donts := disable_re.FindAllStringIndex(str_instructions, -1)
+
+	enabled := true
+	done := false
+
+	start_i := 0
+	end_i := 0
+
+	for !done {
+		if enabled {
+			donts = next(donts, start_i)
+			if donts == nil {
+				total += handle_muls(str_instructions[start_i:])
+				done = true
+			} else {
+				end_i = donts[0][0]
+				total += handle_muls(str_instructions[start_i : end_i+1])
+				enabled = false
+			}
+		} else {
+			dos = next(dos, end_i)
+			if dos == nil {
+				done = true
+			} else {
+				start_i = dos[0][1]
+				enabled = true
+			}
+		}
+	}
+	fmt.Println(dos)
+	fmt.Println(donts)
+	fmt.Println(total)
+}