20/code.go

@@ -0,0 +1,108 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"log"
+	"os"
+)
+
+func readInput(file *os.File) []int {
+	scanner := bufio.NewScanner(file)
+	var numbers []int
+
+	for scanner.Scan() {
+		line := scanner.Text()
+		if line == "" {
+			continue
+		}
+
+		var current int
+		n, err := fmt.Sscanf(line, "%d", &current)
+		if n != 1 || err != nil {
+			log.Fatal("Can't parse:", line, err)
+		}
+
+		numbers = append(numbers, current)
+	}
+
+	return numbers
+}
+
+func indexOf(numbers []int, number int) int {
+	for i := range numbers {
+		if numbers[i] == number {
+			return i
+		}
+	}
+
+	return -1
+}
+
+func establishNewIndex(size int, current int, value int) int {
+	delta := current + value
+	if delta <= 0 {
+		delta = 0 - delta + 1
+		rest := delta % size
+
+		return size - rest
+	}
+
+	if delta >= size {
+		return delta%size + 1
+	}
+
+	return delta
+}
+
+func removeAt(numbers []int, index int) []int {
+	return append(numbers[:index], numbers[index+1:]...)
+}
+
+func addAt(numbers []int, value int, index int) []int {
+	if index >= len(numbers) {
+		return append(numbers, value)
+	}
+
+	var temp []int
+	temp = append(temp, numbers[:index]...)
+	temp = append(temp, value)
+
+	return append(temp, numbers[index:]...)
+}
+
+func mix(numbers []int) []int {
+	size := len(numbers)
+	mixed := make([]int, size)
+	copy(mixed, numbers)
+
+	for i := range numbers {
+		if numbers[i] == 0 {
+			continue
+		}
+
+		currentIndex := indexOf(mixed, numbers[i])
+		newIndex := establishNewIndex(size, currentIndex, numbers[i])
+
+		mixed = removeAt(mixed, currentIndex)
+		mixed = addAt(mixed, numbers[i], newIndex)
+	}
+
+	return mixed
+}
+
+func main() {
+	if len(os.Args) < 2 {
+		log.Fatal("You need to specify a file!")
+	}
+
+	filePath := os.Args[1]
+	file, err := os.Open(filePath)
+	if err != nil {
+		log.Fatalf("Failed to open %s!\n", filePath)
+
+	}
+
+	numbers := readInput(file)
+	fmt.Println(mix(numbers))
+}