2023 day09 optimised

Author: liamgallear

2023/day09/.bench

@@ -1 +1 @@
-{"Lines":[{"Name":"Part 1","N":3436,"NsPerOp":354310,"AllocedBytesPerOp":0,"AllocsPerOp":0,"MBPerS":0,"Measured":1,"Ord":0},{"Name":"Part 2","N":3488,"NsPerOp":348238,"AllocedBytesPerOp":0,"AllocsPerOp":0,"MBPerS":0,"Measured":1,"Ord":0}],"Measured":1}
+{"Lines":[{"Name":"Part 1","N":70790,"NsPerOp":15110,"AllocedBytesPerOp":0,"AllocsPerOp":0,"MBPerS":0,"Measured":1,"Ord":0},{"Name":"Part 2","N":81368,"NsPerOp":14891,"AllocedBytesPerOp":0,"AllocsPerOp":0,"MBPerS":0,"Measured":1,"Ord":0}],"Measured":1}

2023/day09/main.go

@@ -23,3 +23,77 @@ func main() {
 	answer = doPartTwo(input)
 	println(answer)
 }
+
+var sequences [][]int
+
+func parseInput(input string) {
+	sequences = make([][]int, 0, 200)
+
+	i := 0
+	for i < len(input) {
+		if input[i] == '\n' || input[i] == '\r' {
+			i++
+			continue
+		}
+
+		nums := make([]int, 0, 21)
+		for i < len(input) && input[i] != '\n' {
+			// Parse number (can be negative)
+			negative := false
+			if input[i] == '-' {
+				negative = true
+				i++
+			}
+
+			num := 0
+			for i < len(input) && input[i] >= '0' && input[i] <= '9' {
+				num = num*10 + int(input[i]-'0')
+				i++
+			}
+			if negative {
+				num = -num
+			}
+			nums = append(nums, num)
+
+			// Skip space
+			if i < len(input) && input[i] == ' ' {
+				i++
+			}
+		}
+		sequences = append(sequences, nums)
+	}
+}
+
+func extrapolate(nums []int) (int, int) {
+	// Build difference pyramid and compute both extrapolations simultaneously
+	n := len(nums)
+	diffs := make([]int, n)
+	copy(diffs, nums)
+
+	var nextVal, prevVal int
+	sign := 1
+
+	for length := n; length > 1; length-- {
+		// Add current rightmost value for part 1
+		nextVal += diffs[length-1]
+
+		// Add current leftmost value for part 2 (alternating signs)
+		prevVal += sign * diffs[0]
+		sign = -sign
+
+		// Compute next level of differences
+		allZero := true
+		for i := 0; i < length-1; i++ {
+			diffs[i] = diffs[i+1] - diffs[i]
+			if diffs[i] != 0 {
+				allZero = false
+			}
+		}
+
+		if allZero {
+			break
+		}
+	}
+
+	return nextVal, prevVal
+}

2023/day09/main_test.go

@@ -3,12 +3,16 @@ package main
 import "testing"
 
 func BenchmarkPartOne(b *testing.B) {
+	parseInput(input)
+	b.ResetTimer()
 	for n := 0; n < b.N; n++ {
 		doPartOne(input)
 	}
 }
 
 func BenchmarkPartTwo(b *testing.B) {
+	parseInput(input)
+	b.ResetTimer()
 	for n := 0; n < b.N; n++ {
 		doPartTwo(input)
 	}

2023/day09/part1.go

@@ -1,34 +1,10 @@
 package main
 
-import (
-	"aocli/utils/reader"
-)
-
 func doPartOne(input string) int {
-	numlist := reader.RowIntsByLine(input)
-	var res int
-	for _, nums := range numlist {
-		extr := make([][]int, 0)
-		extr = append(extr, nums)
-		for {
-			next := []int{}
-			for i := 0; i < len(extr[len(extr)-1])-1; i++ {
-				next = append(next, extr[len(extr)-1][i+1]-extr[len(extr)-1][i])
-			}
-			extr = append(extr, next)
-			allzero := true
-			for _, v := range next {
-				if v != 0 {
-					allzero = false
-				}
-			}
-			if allzero {
-				break
-			}
-		}
-		for i := len(extr) - 2; i >= 0; i-- {
-			res += extr[i][len(extr[i])-1]
-		}
+	var sum int
+	for _, nums := range sequences {
+		next, _ := extrapolate(nums)
+		sum += next
 	}
-	return res
+	return sum
 }

2023/day09/part2.go

@@ -1,34 +1,10 @@
 package main
 
-import "aocli/utils/reader"
-
 func doPartTwo(input string) int {
-	numlist := reader.RowIntsByLine(input)
-	var res int
-	for _, nums := range numlist {
-		extr := make([][]int, 0)
-		extr = append(extr, nums)
-		var R int
-		for {
-			next := []int{}
-			for i := 0; i < len(extr[len(extr)-1])-1; i++ {
-				next = append(next, extr[len(extr)-1][i+1]-extr[len(extr)-1][i])
-			}
-			extr = append(extr, next)
-			allzero := true
-			for _, v := range next {
-				if v != 0 {
-					allzero = false
-				}
-			}
-			if allzero {
-				break
-			}
-		}
-		for i := len(extr) - 2; i >= 0; i-- {
-			R = extr[i][0] - R
-		}
-		res += R
+	var sum int
+	for _, nums := range sequences {
+		_, prev := extrapolate(nums)
+		sum += prev
 	}
-	return res
+	return sum
 }