🌅

solutions/day20/day20.go

@@ -0,0 +1,144 @@
+package day20
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strconv"
+)
+
+func printNumbers(numbers []int, nexts []int) {
+	current := 0
+
+	for nexts[current] == -1 {
+		current += 1
+	}
+
+	first := numbers[current]
+	fmt.Printf("%d", first)
+	current = nexts[current]
+	for numbers[current] != first {
+		fmt.Printf(" %d", numbers[current])
+		current = nexts[current]
+	}
+	fmt.Println()
+}
+
+func removeIndex(idx int, prevs []int, nexts []int) (before int, after int) {
+	before = prevs[idx]
+	after = nexts[idx]
+
+	nexts[before] = after
+	prevs[after] = before
+	prevs[idx] = -1
+	nexts[idx] = -1
+
+	return
+}
+
+func insertAfter(idx int, after int, prevs []int, nexts []int) {
+	afterNext := nexts[after]
+	prevs[idx] = after
+	nexts[idx] = afterNext
+	prevs[afterNext] = idx
+	nexts[after] = idx
+}
+
+func insertBefore(idx int, before int, prevs []int, nexts []int) {
+	beforePrev := prevs[before]
+	prevs[idx] = beforePrev
+	nexts[idx] = before
+	prevs[before] = idx
+	nexts[beforePrev] = idx
+}
+
+func shift(count int, idx int, prevs []int, nexts []int) {
+	count %= len(prevs) - 1
+	for count != 0 {
+		before, after := removeIndex(idx, prevs, nexts)
+		if count > 0 {
+			insertAfter(idx, after, prevs, nexts)
+			count -= 1
+		} else {
+			insertBefore(idx, before, prevs, nexts)
+			count += 1
+		}
+	}
+}
+
+func indexPast(count int, current int, nexts []int) int {
+	for count > 0 {
+		current = nexts[current]
+		count -= 1
+	}
+	return current
+}
+
+func Run(filename string, keyString string, countString string) {
+	file, err := os.Open(filename)
+	if err != nil {
+		fmt.Println("Error opening file:", err)
+		return
+	}
+
+	key, err := strconv.Atoi(keyString)
+	if err != nil {
+		fmt.Println("Invalid key value", err)
+		return
+	}
+
+	roundCount, err := strconv.Atoi(countString)
+	if err != nil {
+		fmt.Println("Invalid round count", err)
+		return
+	}
+
+	scanner := bufio.NewScanner(file)
+	scanner.Split(bufio.ScanLines)
+	numbers := []int{}
+	nexts := []int{}
+	prevs := []int{}
+	zeroIndex := -1
+
+	for scanner.Scan() {
+		line := scanner.Text()
+		x, err := strconv.Atoi(line)
+		if err != nil {
+			fmt.Println("Couldn't parse number", line)
+			return
+		}
+		numbers = append(numbers, x*key)
+		nexts = append(nexts, 0)
+		prevs = append(prevs, 0)
+
+		if x == 0 {
+			zeroIndex = len(numbers) - 1
+		}
+	}
+
+	for idx := range nexts {
+		nexts[idx] = (idx + 1) % len(nexts)
+		if idx == 0 {
+			prevs[idx] = len(prevs) - 1
+		} else {
+			prevs[idx] = idx - 1
+		}
+	}
+	file.Close()
+
+	for round := 0; round < roundCount; round++ {
+		for idx := range numbers {
+			fmt.Println("Working round", round+1, "index", idx, "with value/count", numbers[idx])
+			shift(numbers[idx], idx, prevs, nexts)
+			//printNumbers(numbers, nexts)
+		}
+	}
+
+	idx1k := indexPast(1000, zeroIndex, nexts)
+	idx2k := indexPast(1000, idx1k, nexts)
+	idx3k := indexPast(1000, idx2k, nexts)
+	val1k := numbers[idx1k]
+	val2k := numbers[idx2k]
+	val3k := numbers[idx3k]
+	fmt.Println("Value 1k after 0", val1k, "2k", val2k, "3k", val3k, "sum", val1k+val2k+val3k)
+}