day 09

2023/day09/main.go

@@ -0,0 +1,128 @@
+package main
+
+import (
+	_ "embed"
+	"flag"
+	"fmt"
+	"strings"
+
+	"github.com/alexchao26/advent-of-code-go/cast"
+	"github.com/alexchao26/advent-of-code-go/util"
+)
+
+//go:embed input.txt
+var input string
+
+func init() {
+	// do this in init (not main) so test file has same input
+	input = strings.TrimRight(input, "\n")
+	if len(input) == 0 {
+		panic("empty input.txt file")
+	}
+}
+
+func main() {
+	var part int
+	flag.IntVar(&part, "part", 1, "part 1 or 2")
+	flag.Parse()
+	fmt.Println("Running part", part)
+
+	if part == 1 {
+		ans := part1(input)
+		util.CopyToClipboard(fmt.Sprintf("%v", ans))
+		fmt.Println("Output:", ans)
+	} else {
+		ans := part2(input)
+		util.CopyToClipboard(fmt.Sprintf("%v", ans))
+		fmt.Println("Output:", ans)
+	}
+}
+
+func part1(input string) int {
+	parsed := parseInput(input)
+	ans := 0
+	for _, hist := range parsed {
+		ans += findNextValue(hist)
+	}
+
+	return ans
+}
+
+func findNextValue(history []int) int {
+	matrix := [][]int{
+		history,
+	}
+	nonZeroFound := true
+	for nonZeroFound {
+		nonZeroFound = false
+		next := []int{}
+
+		matrixHistoryRow := matrix[len(matrix)-1]
+		for i := 1; i < len(matrixHistoryRow); i++ {
+			prev := matrixHistoryRow[i-1]
+			curr := matrixHistoryRow[i]
+			next = append(next, curr-prev)
+			if next[len(next)-1] != 0 {
+				nonZeroFound = true
+			}
+		}
+		matrix = append(matrix, next)
+	}
+
+	ans := 0
+	for _, row := range matrix {
+		ans += row[len(row)-1]
+	}
+
+	return ans
+}
+
+func part2(input string) int {
+	parsed := parseInput(input)
+	ans := 0
+	for _, hist := range parsed {
+		ans += findPrevValue(hist)
+	}
+
+	return ans
+}
+
+func findPrevValue(history []int) int {
+	matrix := [][]int{
+		history,
+	}
+	nonZeroFound := true
+	for nonZeroFound {
+		nonZeroFound = false
+		next := []int{}
+
+		matrixHistoryRow := matrix[len(matrix)-1]
+		for i := 1; i < len(matrixHistoryRow); i++ {
+			prev := matrixHistoryRow[i-1]
+			curr := matrixHistoryRow[i]
+			next = append(next, curr-prev)
+			if next[len(next)-1] != 0 {
+				nonZeroFound = true
+			}
+		}
+		matrix = append(matrix, next)
+	}
+
+	ans := 0
+	for r := len(matrix) - 1; r >= 0; r-- {
+		ans = matrix[r][0] - ans
+	}
+
+	return ans
+}
+
+func parseInput(input string) (ans [][]int) {
+	for _, line := range strings.Split(input, "\n") {
+		nums := []int{}
+		for _, str := range strings.Split(line, " ") {
+			nums = append(nums, cast.ToInt(str))
+		}
+		ans = append(ans, nums)
+	}
+	return ans
+}