AdventOfCode2k16/d04/d04.go

package main

import "strings"
import "strconv"
import "bufio"
import "sort"
import "fmt"
import "os"

type KeyValue struct {
    Key rune
    Value int
}

type KeyValues []KeyValue
func (this KeyValues) Len() int {
    return len(this)
}
func (this KeyValues) Swap(i, j int) {
    tmp := this[i]
    this[i] = this[j]
    this[j] = tmp
}
func (this KeyValues) Less(i, j int) bool {
    if this[i].Value == this[j].Value {
        return this[i].Key > this[j].Key
    }
    return this[i].Value < this[j].Value
}

type Room struct {
    EncryptedName string
    DecryptedName string
    Checksum string
    RoomId int
}

func shiftRune(r rune, shift int) string {
    if r == '-' {
        return " "
    }
    res := int(r) +shift
    if res > 'z' {
        res = res - 'z' + 'a' -1
    }
    return string(res)
}

func NewRoom(roomName string, sectorId int) Room {
    var result Room
    letters := make(map[rune]int)
    letterShift := sectorId %26
    result.EncryptedName = roomName

    for _, l := range(roomName) {
        if (l != '-') {
            letters[l] ++
        }
        result.DecryptedName += shiftRune(l, letterShift)
    }

    sortedLetters := make(KeyValues, len(letters))
    i := 0
    for k, v := range letters {
        sortedLetters[i] = KeyValue{k, v}
        i++
    }
    sort.Sort(sort.Reverse(sortedLetters))

    for i =0; i < 5; i++ {
        result.Checksum += string(sortedLetters[i].Key)
    }

    result.RoomId = sectorId

    return result
}

func (this Room) isValid(checksum string) bool {
    return this.Checksum == checksum
}

func parseLine(line string) (Room, string) {
    words := strings.FieldsFunc(line, func(r rune) bool {
        return (r == '-' || r == '[' || r == ']')
    })

    checkSum := words[len(words) -1]
    sectorId, _ := strconv.Atoi(words[len(words) -2])
    words = words[:len(words) -2]
    var roomName string
    first := true

    for word := range(words) {
        if (first) {
            first = false
        } else {
            roomName += "-"
        }
        roomName += words[word]
    }

    return NewRoom(roomName, sectorId), checkSum
}

func main() {
    reader := bufio.NewReader(os.Stdin)
    valid := 0

    for true {
        line, _, err := reader.ReadLine()

        if string(line) != "" {
            room, checkSum := parseLine(string(line))

            if room.isValid(checkSum) {
                valid += room.RoomId
                if strings.Contains(room.DecryptedName, "northpole") {
                    fmt.Println("Found `North Pole objects` secret room: " +strconv.Itoa(room.RoomId))
                }
            }
        }

        if err != nil {
            break
        }
    }

    fmt.Println(valid)
}