day 17

17/17.go

@@ -0,0 +1,55 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"strconv"
+)
+
+// go run 17.go input
+
+func main() {
+
+	steps,_ := strconv.Atoi(os.Args[1])
+	iterations1 := 2017 
+	iterations2 := 50000000
+
+	fmt.Println(Part1(steps, iterations1))
+	fmt.Println(Part2(steps, iterations2))
+}
+
+func Part1(steps int, iterations int) int {
+	buf := make([]int, iterations+1)
+	buf[0] = 0
+	pos := 0
+
+	for i:=1; i<=iterations; i++ {
+		pos = (pos + steps + 1) % i
+
+		// Move items from top down, insert value into array
+		for j:=i; j > pos; j-- {
+			buf[j] = buf[j-1]
+		}
+		buf[pos+1] = i
+
+	}
+	return buf[pos+2]
+}
+
+func Part2(steps int, iterations int) int {
+	buf := make([]int, iterations+1)
+	buf[0] = 0
+	pos := 0
+	valAfterZero := -1
+
+	for i:=1; i<=iterations; i++ {
+		pos = (pos + steps + 1) % i
+
+		// And zero is always first position in the list, so no need to fiddle with the array...
+		if (pos == 0) {
+			valAfterZero = i
+		}
+
+	}
+	return valAfterZero
+}