day 3 done

day3/main.go

@@ -0,0 +1,78 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"regexp"
+	"strings"
+)
+
+func main() {
+	if len(os.Args) < 2 {
+		panic("Provide input file")
+	}
+	inputFile := os.Args[1]
+
+	part1 := part1(inputFile)
+	fmt.Printf("(%s) Part 1: %d\n", inputFile, part1)
+
+	part2 := part2(inputFile)
+	fmt.Printf("(%s) Part 2: %d\n", inputFile, part2)
+}
+
+func part2(inputFile string) int {
+	input, err := os.ReadFile(inputFile)
+	if err != nil {
+		panic(err)
+	}
+
+	keepParts := make([]string, 0)
+	doParts := strings.Split(string(input), "do()")
+	for _, part := range doParts {
+		keepPart := strings.Split(part, "don't()")[0]
+		keepParts = append(keepParts, keepPart)
+	}
+
+	total := 0
+	for _, part := range keepParts {
+		exp := regexp.MustCompile(`mul\((\d{1,3}),(\d{1,3})\)`)
+		occurrences := exp.FindAllString(string(part), -1)
+		for _, occ := range occurrences {
+			leftExp := regexp.MustCompile(`\((\d{1,3}),`)
+			rightExp := regexp.MustCompile(`,(\d{1,3})\)`)
+			leftNum := leftExp.FindStringSubmatch(occ)[1]
+			rightNum := rightExp.FindStringSubmatch(occ)[1]
+			total += toInt(leftNum) * toInt(rightNum)
+		}
+	}
+	return total
+}
+
+func part1(inputFile string) int {
+	input, err := os.ReadFile(inputFile)
+	if err != nil {
+		panic(err)
+	}
+
+	// regex for finding all mul(###,###) where # can be 1-3 digits
+	exp := regexp.MustCompile(`mul\((\d{1,3}),(\d{1,3})\)`)
+	occurrences := exp.FindAllString(string(input), -1)
+
+	total := 0
+	for _, occ := range occurrences {
+		leftExp := regexp.MustCompile(`\((\d{1,3}),`)
+		rightExp := regexp.MustCompile(`,(\d{1,3})\)`)
+		leftNum := leftExp.FindStringSubmatch(occ)[1]
+		rightNum := rightExp.FindStringSubmatch(occ)[1]
+		total += toInt(leftNum) * toInt(rightNum)
+	}
+	return total
+}
+
+func toInt(s string) int {
+	var num int
+	for _, c := range s {
+		num = num*10 + int(c-'0')
+	}
+	return num
+}

day3/run.sh

@@ -0,0 +1,4 @@
+#!/bin/bash
+
+go build -o ./bin/solution ./main.go
+./bin/solution "$1"