2020-day10: strings.Builder to the rescue again

2015/day10/main.go

@@ -0,0 +1,48 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"strings"
+
+	"github.com/alexchao26/advent-of-code-go/util"
+)
+
+func main() {
+	var part int
+	flag.IntVar(&part, "part", 1, "part 1 or 2")
+	flag.Parse()
+	fmt.Println("Running part", part)
+
+	ans := lookAndSay(util.ReadFile("./input.txt"), part)
+	fmt.Println("Output:", ans)
+}
+
+func lookAndSay(input string, part int) int {
+	lastSaid := input
+
+	rounds := 40
+	if part == 2 {
+		rounds = 50
+	}
+
+	for i := 0; i < rounds; i++ {
+		var runningCount int
+		var said strings.Builder
+
+		for i := 0; i < len(lastSaid); i++ {
+			if i == len(lastSaid)-1 || lastSaid[i] != lastSaid[i+1] {
+				// add to seen
+				said.WriteString(fmt.Sprintf("%d%s", runningCount+1, string(lastSaid[i])))
+				runningCount = 0
+			} else {
+				// build up running count
+				runningCount++
+			}
+
+		}
+		lastSaid = said.String()
+	}
+
+	return len(lastSaid)
+}

2015/day10/main_test.go

@@ -0,0 +1,26 @@
+package main
+
+import (
+	"testing"
+
+	"github.com/alexchao26/advent-of-code-go/util"
+)
+
+func Test_lookAndSay(t *testing.T) {
+	tests := []struct {
+		name  string
+		input string
+		part  int
+		want  int
+	}{
+		{"actual", util.ReadFile("input.txt"), 1, 252594},
+		{"actual", util.ReadFile("input.txt"), 2, 3579328},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := lookAndSay(tt.input, tt.part); got != tt.want {
+				t.Errorf("lookAndSay() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}