From d96d4bd12b42efd621e42c4eca09ee5852e1bc55 Mon Sep 17 00:00:00 2001
From: RPJosh <RPJosh@rpjosh.de>
Date: Sat, 9 Dec 2023 09:33:59 +0100
Subject: [PATCH] 2023: day 9

---
 internal/2023/day_09/in.go | 73 ++++++++++++++++++++++++++++++++++++--
 pkg/utils/utils.go         | 17 +++++++++
 2 files changed, 88 insertions(+), 2 deletions(-)

diff --git a/internal/2023/day_09/in.go b/internal/2023/day_09/in.go
index 4b931f3..3999591 100644
--- a/internal/2023/day_09/in.go
+++ b/internal/2023/day_09/in.go
@@ -1,11 +1,80 @@
 package day_09
 
+import (
+	"fmt"
+	"strings"
+
+	"git.rpjosh.de/RPJosh/go-logger"
+	"rpjosh.de/adventOfCode/pkg/utils"
+)
+
 type Day struct{}
 
 func (d *Day) Part1(in string) string {
-	return ""
+	return d.paseHistories(in, d.extrapolite)
+}
+
+func (d *Day) paseHistories(in string, extrapolite func(vals [][]int) int) string {
+	histories := strings.Split(in, "\n")
+
+	sumExtrapolite := 0
+	for _, history := range histories {
+		if history == "" {
+			continue
+		}
+
+		differences := make([][]int, 0)
+
+		// Calculate differences until we only have zeros
+		vals := utils.ConvertArrayToInt(strings.Split(history, " "))
+		differences = append(differences, vals)
+		for {
+			//logger.Debug("%s", differences)
+			// Do we only have zeros?
+			if utils.AreAllElementsEqual(vals) && vals[0] == 0 {
+				sumExtrapolite += extrapolite(differences)
+				logger.Debug("%d", extrapolite(differences))
+				break
+			}
+
+			// Get the new diffs
+			vals = d.calculateDiffs(vals)
+			differences = append(differences, vals)
+		}
+	}
+
+	return fmt.Sprintf("%d", sumExtrapolite)
+}
+
+// calculateDiffs calculates the difference between two
+// numbers in the provided array and returns a string
+// containing the differences concatenated by a space
+func (d *Day) calculateDiffs(vals []int) (rtc []int) {
+	for i := 0; i < len(vals)-1; i += 1 {
+		rtc = append(rtc, vals[i+1]-vals[i])
+	}
+
+	return rtc
+}
+
+func (d *Day) extrapolite(vals [][]int) int {
+	lastVal := 0
+	for i := len(vals) - 2; i >= 0; i-- {
+		lastVal = lastVal + vals[i][len(vals[i])-1]
+	}
+
+	return lastVal
+}
+
+func (d *Day) extrapoliteFirst(vals [][]int) int {
+	lastVal := 0
+	for i := len(vals) - 2; i >= 0; i-- {
+		lastVal = vals[i][0] - lastVal
+	}
+
+	return lastVal
 }
 
 func (d *Day) Part2(in string) string {
-	return ""
+	return d.paseHistories(in, d.extrapoliteFirst)
 }
diff --git a/pkg/utils/utils.go b/pkg/utils/utils.go
index 6ed5e5b..9e2b2db 100644
--- a/pkg/utils/utils.go
+++ b/pkg/utils/utils.go
@@ -173,3 +173,20 @@ func CalculateLCM(ints ...int) int {
 
 	return CalculateLCM(ints[0], CalculateLCM(ints[1:]...))
 }
+
+func AreAllElementsEqual[T any](vals []T) bool {
+	if len(vals) == 0 {
+		return true
+	}
+
+	prev := vals[0]
+	for i := 0; i < len(vals); i++ {
+		if any(prev) != any(vals[i]) {
+			return false
+		}
+
+		prev = vals[i]
+	}
+
+	return true
+}