and day 25!

25/main.go

@@ -0,0 +1,54 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strconv"
+	"time"
+)
+
+func main() {
+	start := time.Now()
+	partOne()
+	duration := time.Since(start)
+	fmt.Printf("p1: %s, p2: n/a\n", duration)
+}
+
+func partOne() {
+	f, _ := os.Open("input")
+	reader := bufio.NewReader(f)
+	scanner := bufio.NewScanner(reader)
+
+	scanner.Scan()
+	doorPubKey, _ := strconv.Atoi(scanner.Text())
+	scanner.Scan()
+	cardPubKey, _ := strconv.Atoi(scanner.Text())
+
+	subjectNumber := 7
+	value := 1
+	magicPrime := 20201227
+	loopCount := 1
+	doorLoopCount := 0
+	cardLoopCount := 0
+	for {
+		value = (value * subjectNumber) % magicPrime
+		if value == doorPubKey {
+			doorLoopCount = loopCount
+		}
+		if value == cardPubKey {
+			cardLoopCount = loopCount
+		}
+		loopCount = loopCount + 1
+		if doorLoopCount != 0 && cardLoopCount != 0 {
+			break
+		}
+	}
+
+	value = 1
+	subjectNumber = cardPubKey
+	for i := 0; i < doorLoopCount; i = i + 1 {
+		value = (value * subjectNumber) % magicPrime
+	}
+	fmt.Println(value)
+}