Days 7,8,9

2023/gareth/day09/day09.go

@@ -0,0 +1,80 @@
+package day09
+
+import (
+	"strconv"
+	"strings"
+)
+
+func Part1(input string) int {
+	lines := strings.Split(input, "\r\n")
+	total := 0
+	for _, line := range lines {
+		var intSeq []int
+		seq := strings.Split(line, " ")
+		for _, i := range seq {
+			num, _ := strconv.Atoi(i)
+			intSeq = append(intSeq, num)
+		}
+		total += extrapolate1(intSeq)
+	}
+	return total
+}
+
+func Part2(input string) int {
+	lines := strings.Split(input, "\r\n")
+	total := 0
+	for _, line := range lines {
+		var intSeq []int
+		seq := strings.Split(line, " ")
+		for _, i := range seq {
+			num, _ := strconv.Atoi(i)
+			intSeq = append(intSeq, num)
+		}
+		total += extrapolate2(intSeq)
+	}
+	return total
+}
+
+func extrapolate1(array []int) int {
+	allZeros := true
+	for _, x := range array {
+		if x != 0 {
+			allZeros = false
+			break
+		}
+	}
+
+	if allZeros {
+		return 0
+	}
+
+	deltas := make([]int, len(array)-1)
+	for i := 0; i < len(array)-1; i++ {
+		deltas[i] = array[i+1] - array[i]
+	}
+
+	diff := extrapolate1(deltas)
+	return array[len(array)-1] + diff
+}
+
+func extrapolate2(array []int) int {
+	allZeros := true
+	for _, x := range array {
+		if x != 0 {
+			allZeros = false
+			break
+		}
+	}
+
+	if allZeros {
+		return 0
+	}
+
+	deltas := make([]int, len(array)-1)
+	for i := 0; i < len(array)-1; i++ {
+		deltas[i] = array[i+1] - array[i]
+	}
+
+	diff := extrapolate2(deltas)
+	return array[0] - diff
+}