chore(2024): improve performance of day1

go/2024/README.md

@@ -20,10 +20,16 @@ Collect stars by solving puzzles. Two puzzles will be made available on each day
 
 | Day |           #1 |           #2 | Improvement\* |
 | --- | -----------: | -----------: | ------------- |
-| 1   | 120513 ns/op | 415683 ns/op |               |
+| 1   | 120513 ns/op | 155479 ns/op | - / `62.6%`   |
 
 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.
 
+### Previous solutions
+
+| Day |  #1 |           #2 | Improvement | Link                                                                                                                           |
+| --: | --: | -----------: | ----------: | ------------------------------------------------------------------------------------------------------------------------------ |
+|   1 |   - | 415683 ns/op |             | [Link](https://github.com/believer/advent-of-code/blob/47447cc17fffe6994d4b54c4cb815e698b3f5605/go/2024/puzzles/day01/main.go) |
+
 ## Running
 
 Run a day

go/2024/puzzles/day01/main.go

@@ -3,7 +3,6 @@ package main
 import (
 	"fmt"
 	"slices"
-	"strconv"
 	"strings"
 
 	"github.com/believer/aoc-2024/utils"
@@ -17,33 +16,13 @@ func main() {
 }
 
 func part1(name string) int {
-	lines := files.ReadLines(name)
-	left := []int{}
-	right := []int{}
-	total := 0
-
-	for _, line := range lines {
-		row := strings.Split(line, "   ")
-
-		l, err := strconv.Atoi(row[0])
-
-		if err != nil {
-			panic(err)
-		}
-
-		r, err := strconv.Atoi(row[1])
-
-		if err != nil {
-			panic(err)
-		}
-
-		left = append(left, l)
-		right = append(right, r)
-	}
+	left, right := historicallySignificantLocations(name)
 
 	slices.Sort(left)
 	slices.Sort(right)
 
+	total := 0
+
 	for i, l := range left {
 		total += utils.Abs(l - right[i])
 	}
@@ -52,40 +31,46 @@ func part1(name string) int {
 }
 
 func part2(name string) int {
-	lines := files.ReadLines(name)
-	left := []int{}
-	right := []int{}
-	total := 0
+	left, right := historicallySignificantLocations(name)
 
-	for _, line := range lines {
-		row := strings.Split(line, "   ")
+	total := 0
+	appears := map[int]int{}
 
-		l, err := strconv.Atoi(row[0])
+	for _, r := range right {
+		_, ok := appears[r]
 
-		if err != nil {
-			panic(err)
+		if ok {
+			appears[r] += 1
+		} else {
+			appears[r] = 1
 		}
+	}
 
-		r, err := strconv.Atoi(row[1])
+	for _, l := range left {
+		v, ok := appears[l]
 
-		if err != nil {
-			panic(err)
+		if ok {
+			total += l * v
 		}
-
-		left = append(left, l)
-		right = append(right, r)
 	}
 
-	for _, l := range left {
-		appears := 0
-		for _, r := range right {
-			if l == r {
-				appears += 1
-			}
-		}
+	return total
+}
+
+func historicallySignificantLocations(name string) ([]int, []int) {
+	lines := files.ReadLines(name)
+	left := make([]int, len(lines))
+	right := make([]int, len(lines))
+
+	for _, line := range lines {
+		row := strings.Fields(line)
 
-		total += l * appears
+		l := utils.MustIntFromString(row[0])
+		r := utils.MustIntFromString(row[1])
+
+		left = append(left, l)
+		right = append(right, r)
 	}
 
-	return total
+	return left, right
 }

go/2024/utils/utils.go

@@ -20,7 +20,7 @@ func Sum(nums []int) int {
 	return total
 }
 
-func FromString(s string) int {
+func MustIntFromString(s string) int {
 	v, err := strconv.Atoi(s)
 
 	if err != nil {