2016-day04: caesar shift algo, validating checksum

2016/day04/main.go

@@ -0,0 +1,120 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"sort"
+	"strings"
+
+	"github.com/alexchao26/advent-of-code-go/algos"
+	"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)
+
+	if part == 1 {
+		ans := part1(util.ReadFile("./input.txt"))
+		fmt.Println("Output:", ans)
+	} else {
+		ans := part2(util.ReadFile("./input.txt"))
+		fmt.Println("Output:", ans)
+	}
+}
+
+func part1(input string) int {
+	rooms := parseInput(input)
+
+	rooms = getValidRooms(rooms)
+	var sum int
+	for _, rm := range rooms {
+		sum += rm.sectorID
+	}
+
+	return sum
+}
+
+func part2(input string) int {
+	rooms := getValidRooms(parseInput(input))
+
+	for _, rm := range rooms {
+		for i := 0; i < rm.sectorID; i++ {
+			// rotate each character forward
+			for i, part := range rm.nameParts {
+				rm.nameParts[i] = algos.CaesarShift(part, rm.sectorID)
+			}
+			// printed all new name parts and searched for "north" to find what the goal text was
+			if rm.nameParts[0] == "northpole" &&
+				rm.nameParts[1] == "object" &&
+				rm.nameParts[2] == "storage" {
+				return rm.sectorID
+			}
+		}
+	}
+
+	panic("loop should have returned sectorID")
+}
+
+type room struct {
+	nameParts []string
+	sectorID  int
+	checksum  string
+}
+
+func parseInput(input string) (ans []room) {
+	for _, line := range strings.Split(input, "\n") {
+		r := room{}
+		parts := strings.Split(line, "-")
+		r.nameParts = parts[:len(parts)-1]
+		fmt.Sscanf(parts[len(parts)-1], "%d[%5s]", &r.sectorID, &r.checksum)
+
+		ans = append(ans, r)
+	}
+
+	return ans
+}
+
+func getValidRooms(rooms []room) []room {
+	var validRooms []room
+	for _, rm := range rooms {
+		countChars := map[string]int{}
+		for _, part := range rm.nameParts {
+			for _, char := range part {
+				countChars[string(char)]++
+			}
+		}
+		var allCounts []int
+		for _, v := range countChars {
+			allCounts = append(allCounts, v)
+		}
+		// sort in reverse order so five highest are at the front
+		sort.Sort(sort.Reverse((sort.IntSlice(allCounts))))
+
+		isValid := true
+
+		var counts []int
+		for i, char := range rm.checksum {
+			counts = append(counts, countChars[string(char)])
+			// compare to five highest
+			if counts[i] != allCounts[i] {
+				isValid = false
+			}
+
+			// tie break equal counts
+			if i != 0 {
+				if counts[i-1] < counts[i] ||
+					(counts[i-1] == counts[i] && string(rm.checksum[i-1]) > string(char)) {
+					isValid = false
+				}
+			}
+		}
+
+		if isValid {
+			validRooms = append(validRooms, rm)
+		}
+	}
+	return validRooms
+}

2016/day04/main_test.go

@@ -0,0 +1,47 @@
+package main
+
+import (
+	"testing"
+
+	"github.com/alexchao26/advent-of-code-go/util"
+)
+
+var example = `aaaaa-bbb-z-y-x-123[abxyz]
+a-b-c-d-e-f-g-h-987[abcde]
+not-a-real-room-404[oarel]
+totally-real-room-200[decoy]`
+
+func Test_part1(t *testing.T) {
+	tests := []struct {
+		name  string
+		input string
+		want  int
+	}{
+		{"example", example, 1514},
+		{"actual", util.ReadFile("input.txt"), 278221},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := part1(tt.input); got != tt.want {
+				t.Errorf("part1() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
+func Test_part2(t *testing.T) {
+	tests := []struct {
+		name  string
+		input string
+		want  int
+	}{
+		{"actual", util.ReadFile("input.txt"), 267},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := part2(tt.input); got != tt.want {
+				t.Errorf("part2() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}

algos/caesar-shift.go

@@ -0,0 +1,15 @@
+package algos
+
+// CaesarShift performs a forwards caesar shift of a given shiftAmount
+func CaesarShift(in string, shiftAmount int) string {
+	var result string
+	for _, char := range in {
+		// char to ascii number
+		ascii := int(char) - int('a')
+		ascii += shiftAmount
+		ascii %= 26
+		ascii += int('a')
+		result += string(rune(ascii))
+	}
+	return result
+}