From b4de75dc87b5fb4d65f39d7549a356e2aae641a4 Mon Sep 17 00:00:00 2001
From: Ang Chin Han <ang.chin.han@gmail.com>
Date: Fri, 13 Dec 2024 13:42:32 +0800
Subject: [PATCH] feat(angch/2024-13): Initial

---
 angch/2024-13/main.go  | 142 +++++++++++++++++++++++++++++++++++++++++
 angch/2024-13/test.txt |  15 +++++
 2 files changed, 157 insertions(+)
 create mode 100644 angch/2024-13/main.go
 create mode 100644 angch/2024-13/test.txt

diff --git a/angch/2024-13/main.go b/angch/2024-13/main.go
new file mode 100644
index 0000000..b13fa0f
--- /dev/null
+++ b/angch/2024-13/main.go
@@ -0,0 +1,142 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"log"
+	"os"
+	"regexp"
+	"runtime/pprof"
+	"strconv"
+	"time"
+)
+
+func gcd(a, b int) int {
+	for b != 0 {
+		a, b = b, a%b
+	}
+	return a
+}
+
+// Function to calculate the determinant of a 2x2 matrix
+func det(a, b, c, d int) int {
+	return a*d - b*c
+}
+
+func day13(file string) (part1, part2 int) {
+	f, err := os.Open(file)
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer f.Close()
+	scanner := bufio.NewScanner(f)
+	regex := regexp.MustCompile(`Button (\w+): X\+([0-9]+), Y\+([0-9]+)`)
+	regex2 := regexp.MustCompile(`Prize: X=([0-9]+), Y=([0-9]+)`)
+
+	for scanner.Scan() {
+		l1 := scanner.Text()
+		scanner.Scan()
+
+		l2 := scanner.Text()
+		scanner.Scan()
+
+		l3 := scanner.Text()
+		scanner.Scan()
+		buttons := [][2]int{}
+		b1, c1 := 0, 0
+
+		// Parse: Button A: X+31, Y+16
+
+		m := regex.FindStringSubmatch(l1)
+		// log.Printf("%+v", m)
+		b1, _ = strconv.Atoi(m[2])
+		c1, _ = strconv.Atoi(m[3])
+
+		buttons = append(buttons, [2]int{b1, c1})
+
+		m = regex.FindStringSubmatch(l2)
+		// a = m[1]
+		b1, _ = strconv.Atoi(m[2])
+		c1, _ = strconv.Atoi(m[3])
+		buttons = append(buttons, [2]int{b1, c1})
+
+		m = regex2.FindStringSubmatch(l3)
+		b1, _ = strconv.Atoi(m[1])
+		c1, _ = strconv.Atoi(m[2])
+
+		prize := [2]int{b1, c1}
+
+		log.Println(buttons)
+		log.Println("Prize", prize)
+
+		log.Println(gcd(buttons[0][0], prize[0]))
+		buttona := buttons[0]
+		buttonb := buttons[1]
+
+		// sum := 0
+		x1, x2 := buttona[0], buttonb[0]
+		y1, y2 := buttona[1], buttonb[1]
+		x3, y3 := prize[0], prize[1]
+		// Calculate the determinant of the coefficient matrix
+		D := det(x1, x2, y1, y2)
+		if D == 0 {
+			fmt.Println("No unique solution exists.")
+		} else {
+			// Calculate the determinants for a and b
+			Da := det(x3, x2, y3, y2)
+			Db := det(x1, x3, y1, y3)
+			// Solve for a and b using Cramer's rule
+			a := Da / D
+			b := Db / D
+
+			if a*x1+b*x2 == x3 && a*y1+b*y2 == y3 {
+				fmt.Printf("The solution is: a = %d, b = %d\n", a, b)
+				part1 += a*3 + b
+			} else {
+				fmt.Println("The solution is incorrect.")
+			}
+		}
+
+		x3, y3 = x3+10000000000000, y3+10000000000000
+		// Calculate the determinants for a and b
+		Da := det(x3, x2, y3, y2)
+		Db := det(x1, x3, y1, y3)
+		// Solve for a and b using Cramer's rule
+		a := Da / D
+		b := Db / D
+
+		if a*x1+b*x2 == x3 && a*y1+b*y2 == y3 {
+			fmt.Printf("The solution is: a = %d, b = %d\n", a, b)
+			part2 += a*3 + b
+		} else {
+			fmt.Println("The solution is incorrect.")
+		}
+	}
+
+	return
+}
+
+func main() {
+	log.SetFlags(log.Lshortfile | log.LstdFlags)
+	logperf := false
+	if logperf {
+		pf, _ := os.Create("default.pgo")
+		err := pprof.StartCPUProfile(pf)
+		if err != nil {
+			log.Fatal(err)
+		}
+		defer pf.Close()
+	}
+	t1 := time.Now()
+	part1, part2 := day13("test.txt")
+	fmt.Println(part1, part2)
+	if part1 != 480 || part2 != 875318608908 {
+		log.Fatal("Test failed ", part1, part2)
+	}
+	fmt.Println(day13("input.txt"))
+	if logperf {
+		pprof.StopCPUProfile()
+	}
+
+	fmt.Println("Elapsed time:", time.Since(t1))
+}
diff --git a/angch/2024-13/test.txt b/angch/2024-13/test.txt
new file mode 100644
index 0000000..912f482
--- /dev/null
+++ b/angch/2024-13/test.txt
@@ -0,0 +1,15 @@
+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