Add solution for day 9 part 2

day9/main.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"io"
 	"os"
+	"slices"
 	"strconv"
 	"strings"
 )
@@ -35,6 +36,7 @@ func main() {
 	}
 
 	fmt.Printf("Part 1: %d\n", part1(histories))
+	fmt.Printf("Part 2: %d\n", part2(histories))
 }
 
 func part1(histories [][]int) int {
@@ -46,6 +48,17 @@ func part1(histories [][]int) int {
 	return total
 }
 
+func part2(histories [][]int) int {
+	total := 0
+	for _, history := range histories {
+		reversedHistory := slices.Clone(history)
+		slices.Reverse(reversedHistory)
+		total += predictNextValue(reversedHistory)
+	}
+
+	return total
+}
+
 // predictNextValue calculates the next item in the sequence by using the nth differences
 func predictNextValue(history []int) int {
 	if allEqual(history, 0) {