perf(2024): parallelize day 7 for major speed improvements

believer · Dec 7, 2024 · a91d614 · a91d614
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diff --git a/go/2024/README.md b/go/2024/README.md
@@ -26,28 +26,29 @@ Collect stars by solving puzzles. Two puzzles will be made available on each day
 
 Using Go's built-in benchmarking with the [testing](https://pkg.go.dev/testing#hdr-Benchmarks) package. Computer is a 2021 MacBook Pro M1 Pro, 32 GB RAM.
 
-| Day |              #1 |               #2 | Improvement\*       |
-| --- | --------------: | ---------------: | ------------------- |
-| 1   |    116264 ns/op |     131233 ns/op | `3.53%` / `68.43%`  |
-| 2   |    310935 ns/op |     723512 ns/op |                     |
-| 3   |    336448 ns/op |     785320 ns/op | - / `36.98%`        |
-| 4   |    523315 ns/op |     217584 ns/op | `81.73%` / `26.09%` |
-| 5   |    778880 ns/op |    3129873 ns/op | `53.34%` / `81.91%` |
-| 6   |    312461 ns/op | 1153391125 ns/op |                     |
-| 7   | 110164692 ns/op | 7135839625 ns/op | `13.18%` / `29.52%` |
+| Day |             #1 |               #2 | Improvement\*       |
+| --- | -------------: | ---------------: | ------------------- |
+| 1   |   116264 ns/op |     131233 ns/op | `3.53%` / `68.43%`  |
+| 2   |   310935 ns/op |     723512 ns/op |                     |
+| 3   |   336448 ns/op |     785320 ns/op | - / `36.98%`        |
+| 4   |   523315 ns/op |     217584 ns/op | `81.73%` / `26.09%` |
+| 5   |   778880 ns/op |    3129873 ns/op | `53.34%` / `81.91%` |
+| 6   |   312461 ns/op | 1153391125 ns/op |                     |
+| 7   | 16480300 ns/op |  842853000 ns/op | `87.01%` / `91.67%` |
 
 \* compared to first solution
 
 ### Previous solutions
 
-| Day |              #1 |                #2 |  Improvement | Link                                                                                                                           |
-| --: | --------------: | ----------------: | -----------: | ------------------------------------------------------------------------------------------------------------------------------ |
-|   1 |    120513 ns/op |      415683 ns/op |     Baseline | [Link](https://github.com/believer/advent-of-code/blob/47447cc17fffe6994d4b54c4cb815e698b3f5605/go/2024/puzzles/day01/main.go) |
-|   1 |    120513 ns/op |      155479 ns/op | - / `62,59%` | [Link](https://github.com/believer/advent-of-code/blob/ea42592462771b74de87eae6bea9c0ca892a4499/go/2024/puzzles/day01/main.go) |
-|   3 |    336448 ns/op |     1246155 ns/op |     Baseline | [Link](https://github.com/believer/advent-of-code/blob/461c2dd40039c27102aa1790c650decb79d4f549/go/2024/puzzles/day03/main.go) |
-|   4 |   2864606 ns/op |      294413 ns/op |     Baseline | [Link](https://github.com/believer/advent-of-code/blob/99909bb30f82cda079471134452d886a0eb6266f/go/2024/puzzles/day04/main.go) |
-|   5 |   1669175 ns/op |    17299190 ns/op |     Baseline | [Link](https://github.com/believer/advent-of-code/blob/1db858ae3d391319511787d8935c76eecdf6b22f/go/2024/puzzles/day05/main.go) |
-|   7 | 126892714 ns/op | 10124683583 ns/op |     Baseline | [Link](https://github.com/believer/advent-of-code/blob/dd735747021ce43ca3a7427c529813139737271e/go/2024/puzzles/day07/main.go) |
+| Day |              #1 |                #2 |         Improvement | Link                                                                                                                           |
+| --: | --------------: | ----------------: | ------------------: | ------------------------------------------------------------------------------------------------------------------------------ |
+|   1 |    120513 ns/op |      415683 ns/op |            Baseline | [Link](https://github.com/believer/advent-of-code/blob/47447cc17fffe6994d4b54c4cb815e698b3f5605/go/2024/puzzles/day01/main.go) |
+|   1 |    120513 ns/op |      155479 ns/op |        - / `62,59%` | [Link](https://github.com/believer/advent-of-code/blob/ea42592462771b74de87eae6bea9c0ca892a4499/go/2024/puzzles/day01/main.go) |
+|   3 |    336448 ns/op |     1246155 ns/op |            Baseline | [Link](https://github.com/believer/advent-of-code/blob/461c2dd40039c27102aa1790c650decb79d4f549/go/2024/puzzles/day03/main.go) |
+|   4 |   2864606 ns/op |      294413 ns/op |            Baseline | [Link](https://github.com/believer/advent-of-code/blob/99909bb30f82cda079471134452d886a0eb6266f/go/2024/puzzles/day04/main.go) |
+|   5 |   1669175 ns/op |    17299190 ns/op |            Baseline | [Link](https://github.com/believer/advent-of-code/blob/1db858ae3d391319511787d8935c76eecdf6b22f/go/2024/puzzles/day05/main.go) |
+|   7 | 126892714 ns/op | 10124683583 ns/op |            Baseline | [Link](https://github.com/believer/advent-of-code/blob/dd735747021ce43ca3a7427c529813139737271e/go/2024/puzzles/day07/main.go) |
+|   7 | 110164692 ns/op |  7135839625 ns/op | `13.18%` / `29.52%` | [Link](https://github.com/believer/advent-of-code/blob/640d9604dfefa71f7bfef876750f378bd1a58a8b/go/2024/puzzles/day07/main.go) |
 
 ## Running
 

diff --git a/go/2024/puzzles/day07/main.go b/go/2024/puzzles/day07/main.go
@@ -4,137 +4,124 @@ import (
 	"fmt"
 	"strconv"
 	"strings"
+	"sync"
 
 	"github.com/believer/aoc-2024/utils"
 	"github.com/believer/aoc-2024/utils/files"
 )
 
+// Parallelization in Go is so nice and easy and provided a major speed-up
+// in this case.
+
+// Also reducing the amount of type conversions in the permutation
+// generation made some improvement. We used to give it a []string and get back []string.
+// The strings needed to be broken down into individual parts for calculations, so we
+// could instead return a [][]string directly from the permutations.
 func main() {
 	fmt.Println("Part 1: ", part1("input.txt"))
 	fmt.Println("Part 2: ", part2("input.txt"))
 }
 
 func part1(name string) int {
 	lines := files.ReadLines(name)
-	calibrationResult := 0
 	operators := []string{"+", "*"}
 
-expression:
-	for _, l := range lines {
-		result, valuesAsString, _ := strings.Cut(l, ":")
-		values := strings.Split(strings.TrimSpace(valuesAsString), " ")
-		testValue := utils.MustIntFromString(result)
+	return processLines(lines, operators)
+}
 
-		permutations := allPermutations(values, operators)
+func part2(name string) int {
+	lines := files.ReadLines(name)
+	operators := []string{"+", "*", "||"}
 
-		for _, expression := range permutations {
-			total := 0
-			operation := "+"
+	return processLines(lines, operators)
+}
 
-			for _, v := range strings.Split(expression, " ") {
-				if v == "+" {
-					operation = "+"
-					continue
-				}
+// Each line is an independent expression, we can calculate them in parallel
+func processLines(lines, operators []string) int {
+	results := make(chan int, len(lines))
 
-				if v == "*" {
-					operation = "*"
-					continue
-				}
+	var wg sync.WaitGroup
 
-				if operation == "+" {
-					total += utils.MustIntFromString(v)
-				}
+	for _, line := range lines {
+		wg.Add(1)
 
-				if operation == "*" {
-					total *= utils.MustIntFromString(v)
-				}
-			}
+		go func(line string) {
+			defer wg.Done()
+			calibrationResult := evaluateLine(line, operators)
+			results <- calibrationResult
+		}(line)
+	}
 
-			if total == testValue {
-				calibrationResult += total
-				continue expression
-			}
-		}
+	go func() {
+		wg.Wait()
+		close(results)
+	}()
+
+	total := 0
+
+	for result := range results {
+		total += result
 	}
 
-	return calibrationResult
+	return total
 }
 
-func part2(name string) int {
-	lines := files.ReadLines(name)
-	calibrationResult := 0
-	operators := []string{"+", "*", "||"}
+func evaluateLine(line string, operators []string) int {
+	resultAsString, valuesAsString, _ := strings.Cut(line, ":")
+	values := strings.Split(strings.TrimSpace(valuesAsString), " ")
+	result := utils.MustIntFromString(resultAsString)
 
-expression:
-	for _, l := range lines {
-		result, valuesAsString, _ := strings.Cut(l, ":")
-		values := strings.Split(strings.TrimSpace(valuesAsString), " ")
-		testValue := utils.MustIntFromString(result)
-
-		permutations := allPermutations(values, operators)
-
-		for _, expression := range permutations {
-			total := 0
-			operation := "+"
-
-			for _, v := range strings.Split(expression, " ") {
-				if v == "+" {
-					operation = "+"
-					continue
-				}
-
-				if v == "*" {
-					operation = "*"
-					continue
-				}
-
-				if v == "||" {
-					operation = "||"
-					continue
-				}
-
-				if operation == "+" {
-					total += utils.MustIntFromString(v)
-				}
-
-				if operation == "*" {
-					total *= utils.MustIntFromString(v)
-				}
-
-				if operation == "||" {
-					total = utils.MustIntFromString(strconv.Itoa(total) + v)
-				}
+	permutations := allPermutations(values, operators)
+
+	for _, expression := range permutations {
+		total := 0
+		operation := "+"
+
+		for _, v := range expression {
+			switch v {
+			case "+", "*", "||":
+				operation = v
+				continue
 			}
 
-			if total == testValue {
-				calibrationResult += total
-				continue expression
+			num := utils.MustIntFromString(v)
+
+			switch operation {
+			case "+":
+				total += num
+			case "*":
+				total *= num
+			case "||":
+				total = utils.MustIntFromString(strconv.Itoa(total) + v)
 			}
 		}
+
+		if total == result {
+			return total
+		}
 	}
 
-	return calibrationResult
+	return 0
 }
 
-func allPermutations(nums []string, ops []string) []string {
+func allPermutations(nums []string, ops []string) [][]string {
 	if len(nums) == 0 {
 		return nil
 	}
 
-	result := []string{}
-	generateExpressions(nums, ops, nums[0], 1, &result)
+	result := [][]string{}
+	generateExpressions(nums, ops, []string{nums[0]}, 1, &result)
 	return result
 }
 
-func generateExpressions(nums []string, ops []string, current string, index int, result *[]string) {
+func generateExpressions(nums []string, ops []string, current []string, index int, result *[][]string) {
 	if index == len(nums) {
 		*result = append(*result, current)
 		return
 	}
 
 	for _, op := range ops {
-		next := current + " " + op + " " + nums[index]
+		next := append(current, op, nums[index])
 		generateExpressions(nums, ops, next, index+1, result)
 	}
 }