2021 Day 2

2021/day2/main.go

@@ -0,0 +1,89 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+)
+
+type position struct {
+	h, d, aim int
+}
+
+func (p position) move1(op string, n int) position {
+	switch op {
+	case "forward":
+		return position{h: p.h + n, d: p.d}
+	case "up":
+		return position{h: p.h, d: p.d - n}
+	case "down":
+		return position{h: p.h, d: p.d + n}
+	}
+	panic(fmt.Sprintf("Unknown operand: %s", op))
+}
+
+func part1(lines []string) int {
+	var pos position
+	for _, line := range lines {
+		fs := strings.Fields(line)
+		if len(fs) != 2 {
+			panic(fs)
+		}
+		op := fs[0]
+		n, err := strconv.Atoi(fs[1])
+		if err != nil {
+			panic(err)
+		}
+		pos = pos.move1(op, n)
+	}
+	return pos.h * pos.d
+}
+
+func (p position) move2(op string, n int) position {
+	switch op {
+	case "forward":
+		return position{h: p.h + n, d: p.d + n*p.aim, aim: p.aim}
+	case "up":
+		return position{h: p.h, d: p.d, aim: p.aim - n}
+	case "down":
+		return position{h: p.h, d: p.d, aim: p.aim + n}
+	}
+	panic(fmt.Sprintf("Unknown operand: %s", op))
+}
+
+func part2(lines []string) int {
+	var pos position
+	for _, line := range lines {
+		fs := strings.Fields(line)
+		if len(fs) != 2 {
+			panic(fs)
+		}
+		op := fs[0]
+		n, err := strconv.Atoi(fs[1])
+		if err != nil {
+			panic(err)
+		}
+		pos = pos.move2(op, n)
+	}
+	return pos.h * pos.d
+}
+
+func main() {
+	f, err := os.Open("./input/day2.txt")
+	if err != nil {
+		panic(err)
+	}
+
+	scanner := bufio.NewScanner(f)
+	scanner.Split(bufio.ScanLines)
+	var lines []string
+
+	for scanner.Scan() {
+		lines = append(lines, scanner.Text())
+	}
+
+	fmt.Println(part1(lines))
+	fmt.Println(part2(lines))
+}