2016-day9: really... ugly... dfs string parsing algo

2016/day09/main.go

@@ -0,0 +1,49 @@
+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 := decompressLength(util.ReadFile("./input.txt"), part)
+	fmt.Println("Output:", ans)
+}
+
+// well...... this is gross.......
+func decompressLength(in string, part int) int {
+	var decompressedLen int
+	for i := 0; i < len(in); {
+		switch in[i] {
+		case '(':
+			// find index of closing paren, then find total length of substring
+			relativeCloseIndex := strings.Index(in[i:], ")")
+			closeIndex := relativeCloseIndex + i
+
+			var copyLen, repeat int
+			fmt.Sscanf(in[i:closeIndex+1], "(%dx%d)", &copyLen, &repeat)
+
+			substring := in[closeIndex+1 : closeIndex+1+copyLen]
+			patternLength := len(substring)
+			if part == 2 {
+				patternLength = decompressLength(substring, 2)
+			}
+			decompressedLen += patternLength * repeat
+			// jump the closed paren (+1) the length of the substring from THIS
+			// function call
+			i = closeIndex + 1 + len(substring)
+		default:
+			decompressedLen++
+			i++
+		}
+	}
+	return decompressedLen
+}

2016/day09/main_test.go

@@ -0,0 +1,31 @@
+package main
+
+import (
+	"testing"
+
+	"github.com/alexchao26/advent-of-code-go/util"
+)
+
+func Test_decompressLength(t *testing.T) {
+	tests := []struct {
+		name  string
+		input string
+		part  int
+		want  int
+	}{
+		{"example part1_0", "ADVENT", 1, len("ADVENT")},
+		{"example part1_1", "A(1x5)BC", 1, len("ABBBBBC")},
+		{"example part1_2", "(6x1)(1x3)A", 1, len("(1x3)A")},
+		{"actual part1", util.ReadFile("input.txt"), 1, 107035},
+		{"example part2_1", "X(8x2)(3x3)ABCY", 2, len("XABCABCABCABCABCABCY")},
+		{"example part2_2", "(25x3)(3x3)ABC(2x3)XY(5x2)PQRSTX(18x9)(3x2)TWO(5x7)SEVEN", 2, 445},
+		{"actual part2", util.ReadFile("input.txt"), 2, 11451628995},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := decompressLength(tt.input, tt.part); got != tt.want {
+				t.Errorf("decompressLength() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}