2024 Day 13 Complete!

2024/day13/main.go

@@ -0,0 +1,93 @@
+package main
+
+import (
+	"fmt"
+	"math"
+
+	h "git.bullercodeworks.com/brian/adventofcode/helpers"
+)
+
+func main() {
+	inp := h.StdinToStringSlice()
+	part1(inp)
+	fmt.Println()
+	part2(inp)
+}
+
+func part1(inp []string) {
+	fmt.Println("# Part 1")
+	games := parseInput(inp)
+	var total int
+	for i := range games {
+		tokens := games[i].Solve()
+		if tokens > 0 {
+			total = total + tokens
+		}
+	}
+	fmt.Println("Total Tokens:", total)
+}
+
+func part2(inp []string) {
+	fmt.Println("# Part 2")
+	games := parseInput(inp)
+	var total int
+	for i := range games {
+		games[i].Prize.X += 10000000000000
+		games[i].Prize.Y += 10000000000000
+		tokens := games[i].Solve()
+		if tokens > 0 {
+			total = total + tokens
+		}
+	}
+	fmt.Println("Total Tokens:", total)
+}
+
+type Game struct {
+	Line1 h.Coordinate
+	Line2 h.Coordinate
+	Prize h.Coordinate
+}
+
+/*
+Our answer is, in algebraic terms:
+(g.Line1.X * n) + (g.Line2.X * m) = g.Prize.X
+(g.Line1.Y * n) + (g.Line2.Y * m) = g.Prize.Y
+where n is the number of 'A' button presses
+and m is the number of 'B' button presses
+
+Solving for n & m gives us these formulas:
+n = (g.Prize.X * g.Line2.Y - g.Prize.Y * g.Line2.X) / (g.Line1.X * g.Line2.Y - g.Line2.x * g.Line1.Y)
+m = (g.Prize.X - g.Line1.X * n) / g.Line2.X
+Then just make sure that n and m are integers
+*/
+func (g *Game) Solve() int {
+	n := float64(g.Prize.X*g.Line2.Y-g.Prize.Y*g.Line2.X) / float64(g.Line1.X*g.Line2.Y-g.Line2.X*g.Line1.Y)
+	m := (float64(g.Prize.X) - float64(g.Line1.X)*n) / float64(g.Line2.X)
+	if math.Mod(n, 1) != 0 || math.Mod(m, 1) != 0 {
+		return -1
+	}
+	return int(n)*3 + int(m)
+}
+
+func parseInput(inp []string) []Game {
+	var res []Game
+	for i := 0; i < len(inp); {
+		var line1, line2, prize h.Coordinate
+		fmt.Sscanf(inp[i], "Button A: X+%d, Y+%d", &line1.X, &line1.Y)
+		fmt.Sscanf(inp[i+1], "Button B: X+%d, Y+%d", &line2.X, &line2.Y)
+		fmt.Sscanf(inp[i+2], "Prize: X=%d, Y=%d", &prize.X, &prize.Y)
+		g := Game{
+			Line1: line1, Line2: line2, Prize: prize,
+		}
+		res = append(res, g)
+		i = i + 4
+	}
+	return res
+}
+
+func (g Game) String() string {
+	res := fmt.Sprintf("Button A: X+%d, Y+%d\n", g.Line1.X, g.Line1.Y)
+	res = fmt.Sprintf("%sButton B: X+%d, Y+%d\n", res, g.Line2.X, g.Line2.Y)
+	res = fmt.Sprintf("%sPrize: X=%d, Y=%d", res, g.Prize.X, g.Prize.Y)
+	return res
+}

2024/day13/testinput

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+Button A: X+94, Y+34
+Button B: X+22, Y+67
+Prize: X=8400, Y=5400
+
+Button A: X+26, Y+66
+Button B: X+67, Y+21
+Prize: X=12748, Y=12176
+
+Button A: X+17, Y+86
+Button B: X+84, Y+37
+Prize: X=7870, Y=6450
+
+Button A: X+69, Y+23
+Button B: X+27, Y+71
+Prize: X=18641, Y=10279