remove the other cases where we don't need to walk the string

02/main.go

@@ -5,7 +5,6 @@ import (
 	"fmt"
 	"os"
 	"strconv"
-	"strings"
 	"time"
 )
 
@@ -83,11 +82,21 @@ func partOne() {
 		line := scanner.Text()
 		ok := true
 		round++
-		_, draws, _ := strings.Cut(line, ": ")
-		for _, draws := range strings.Split(draws, "; ") {
-			g := parseRound(draws)
-			if g.red > max.red || g.blue > max.blue || g.green > max.green {
-				ok = false
+		for i, c := range line {
+			if c == ':' {
+				line = line[i+2:]
+				break
+			}
+		}
+		var start, end int
+		for i, c := range line {
+			if c == ';' || i == len(line)-1 {
+				end = i + 1
+				g := parseRound(line[start:end])
+				if g.red > max.red || g.blue > max.blue || g.green > max.green {
+					ok = false
+				}
+				start = i + 2
 			}
 		}
 		if ok {
@@ -103,18 +112,28 @@ func partTwo() {
 	sum := 0
 	for scanner.Scan() {
 		line := scanner.Text()
-		_, draws, _ := strings.Cut(line, ": ")
+		for i, c := range line {
+			if c == ':' {
+				line = line[i+2:]
+				break
+			}
+		}
 		max := game{}
-		for _, draws := range strings.Split(draws, "; ") {
-			g := parseRound(draws)
-			if g.red > max.red {
-				max.red = g.red
-			}
-			if g.blue > max.blue {
-				max.blue = g.blue
-			}
-			if g.green > max.green {
-				max.green = g.green
+		var start, end int
+		for i, c := range line {
+			if c == ';' || i == len(line)-1 {
+				end = i + 1
+				g := parseRound(line[start:end])
+				if g.red > max.red {
+					max.red = g.red
+				}
+				if g.blue > max.blue {
+					max.blue = g.blue
+				}
+				if g.green > max.green {
+					max.green = g.green
+				}
+				start = i + 2
 			}
 		}
 		sum += max.blue * max.green * max.red