Solution for day 3 (optimized and working)

day03/Notes.md

@@ -11,6 +11,8 @@
 - 12 instead of 2
 - "just" generalize approach from Level 1 to use 12 instead of 2 digits
 
+__Example for 24-char input and 5 digits:__
+
 ### Attempts
 
 - 154932365400342: too low

day03/main.go

@@ -4,7 +4,6 @@ import (
 	"fmt"
 	"log"
 	"os"
-	"slices"
 	"strconv"
 	"strings"
 )
@@ -41,60 +40,71 @@ func readBanks(fileName string) []string {
 func maxJolts(digits int, banks <-chan string, results chan<- int) {
 	for bank := range banks {
 		remaining := bank
+		var substring string
 
-		// collect potential substrings
-		var substrings []string
-
+		// find substring
 		// loop through digits from 9 to 1
 		for i := 9; i > 0; i-- {
 			digit := strconv.Itoa(i)
 
-			// determine indexes for digit
-			indexes := allIndexes(remaining, digit)
-			if len(indexes) == 0 {
+			// determine first index of digit
+			index := strings.Index(remaining, digit)
+			if index == -1 {
 				continue
 			}
 
-			// find all substrings that could potentially contain the largest
-			// combination of digits (strings that are at least 12 chars long)
-			substrings = []string{}
-
-			for _, index := range indexes {
-				substring := remaining[index:]
-				if len(substring) >= digits {
-					substrings = append(substrings, substring)
-				}
-			}
-
-			// if substrings have been found, there's no need to search for
-			// substrings for a lower digit, so the loop can be exited
-			if len(substrings) > 0 {
+			// ignore everything before digit index
+			substring = remaining[index:]
+			if len(substring) >= digits {
 				break
 			}
 		}
 
-		candidates := []int{}
-
-		for _, substring := range substrings {
-			if len(substring) > digits {
-				// replace digits one by one, from 1 to 9, until substring
-				// has a length of `digits` and therefore qualifies as candidate
-				for i := 1; i <= 9; i++ {
-					digit := strconv.Itoa(i)
-					for strings.Contains(substring, digit) && len(substring) > digits {
-						substring = strings.Replace(substring, digit, "", 1)
-					}
-				}
-			}
-
-			// add candidate
-			candidate, _ := strconv.Atoi(substring)
-			candidates = append(candidates, candidate)
+		// done if length is `digits`
+		if len(substring) == digits {
+			result, _ := strconv.Atoi(substring)
+			results <- result
+			return
 		}
 
-		// out of all candidates, the biggest one is the result for this bank
-		result := slices.Max(candidates)
-		results <- result
+		built := ""
+
+		for i := 9; i > 0; i-- {
+			// done if length is `digits``
+			if len(built) == digits {
+				break
+			}
+
+			for j := 9; j > 0; j-- {
+				digit := strconv.Itoa(j)
+
+				indexes := allIndexes(substring, digit)
+				if len(indexes) == 0 {
+					continue
+				}
+
+				index := strings.Index(substring, digit)
+
+				// continue is resulting substring is too short
+				if len(built)+len(substring[index:]) < digits {
+					continue
+				}
+
+				built += digit
+				substring = substring[index+1:]
+
+				// reset loops
+				j = 10
+				i = 10
+
+				// done
+				if len(built) == digits {
+					result, _ := strconv.Atoi(built)
+					results <- result
+					return
+				}
+			}
+		}
 	}
 }