advent2022/solutions/day5/day5.go

package day5

import (
	"bufio"
	"errors"
	"fmt"
	"os"
	"strconv"
	"strings"
	"unicode"
)

type Stack struct {
	identity rune
	then     *Stack
}

func newStack() *Stack {
	return nil
}

func push(box rune, stack *Stack) *Stack {
	var retval *Stack = new(Stack)
	retval.identity = box
	retval.then = stack
	return retval
}

func pushToEnd(box rune, stack *Stack) *Stack {
	if stack == nil {
		retval := new(Stack)
		retval.identity = box
		retval.then = nil
		return retval
	} else {
		stack.then = pushToEnd(box, stack.then)
		return stack
	}
}

func pushSet(front *Stack, stack *Stack) *Stack {
	var prev *Stack = nil
	current := front

	for current != nil {
		prev = current
		current = current.then
	}

	if prev == nil {
		return stack
	} else {
		prev.then = stack
	}

	return front
}

func pop(stack *Stack) (newStack *Stack, value rune, err error) {
	if stack == nil {
		newStack = nil
		value = 'X'
		err = errors.New("attempt to pop from empty stack")
		return
	}

	value = stack.identity
	newStack = stack.then
	return
}

func popSet(amt int, stack *Stack) (newStack *Stack, set *Stack, err error) {
	var prev *Stack = nil
	var current *Stack = stack

	for i := 0; i < amt; i++ {
		if current == nil {
			err = errors.New("tried to take more items than existed in stack")
			return
		}

		prev = current
		current = current.then
	}

	if prev != nil {
		set = stack
		prev.then = nil
	} else {
		set = nil
	}
	newStack = current

	return
}

func stackLength(stack *Stack) int {
	if stack == nil {
		return 0
	} else {
		return 1 + stackLength(stack.then)
	}
}

type Workspace []*Stack

func addLine(line string, input *Workspace) (err error) {
	currentColumn := 0

	fmt.Println("Workspace line's length is", len(line))
	for len(line) >= 3 {
		fmt.Println("  line length now", len(line))
		// make sure we've got enough space in the workspace
		for currentColumn+1 >= len(*input) {
			*input = append(*input, newStack())
		}

		// see if there's actually something there
		if line[0] == '[' && unicode.IsLetter(rune(line[1])) {
			fmt.Println("Adding", rune(line[1]), "to column", currentColumn)
			(*input)[currentColumn] = pushToEnd(rune(line[1]), (*input)[currentColumn])
		} else if line[0] != ' ' {
			err = errors.New("doesn't start with square or blank")
			return
		}

		currentColumn += 1
		if len(line) == 3 {
			return
		}

		if len(line) > 3 {
			line = line[4:]
		}
	}

	return
}

func runMove(problem int, move OperatorMove, workspace *Workspace) error {
	switch problem {
	case 1:
		for i := 0; i < move.count; i++ {
			newFrom, value, err := pop((*workspace)[move.from])
			if err != nil {
				return err
			}
			(*workspace)[move.from] = newFrom
			(*workspace)[move.to] = push(value, (*workspace)[move.to])
		}
		return nil

	case 2:
		newFrom, poppedSet, err := popSet(move.count, (*workspace)[move.from])
		if err != nil {
			return err
		}
		(*workspace)[move.from] = newFrom
		(*workspace)[move.to] = pushSet(poppedSet, (*workspace)[move.to])
		return nil

	default:
		return errors.New("weird problem number found in runMove")
	}
}

func printWorkspace(input Workspace) {
	maxLength := 0

	for _, element := range input {
		current := stackLength(element)
		if current > maxLength {
			maxLength = current
		}
	}

	for _, element := range input {
		current := stackLength(element)
		blanks := maxLength - current
		outputString := ""

		for i := 0; i < blanks; i++ {
			outputString = outputString + "    "
		}

		node := element
		for node != nil {
			outputString = outputString + fmt.Sprintf("[%c] ", node.identity)
			node = node.then
		}

		fmt.Println(outputString)
	}

}

type OperatorMove struct {
	count int
	from  int
	to    int
}

func parseMove(line string) (move OperatorMove, err error) {
	words := strings.Split(line, " ")

	if len(words) != 6 {
		err = errors.New("wrong number of words in move line")
		return
	}

	if words[0] != "move" || words[2] != "from" || words[4] != "to" {
		err = fmt.Errorf("illegal words in move line: %s/%s/%s", words[0], words[2], words[4])
		return
	}

	count, cerr := strconv.Atoi(words[1])
	from, ferr := strconv.Atoi(words[3])
	to, terr := strconv.Atoi(words[5])

	if cerr != nil || ferr != nil || terr != nil {
		err = fmt.Errorf("illegal number found: %s/%s/%s", words[1], words[3], words[5])
	}

	move = OperatorMove{count, from - 1, to - 1}

	return
}

func Run(filename string, problemStr string) {
	problem, err := strconv.Atoi(problemStr)
	if err != nil || (problem < 1 || problem > 2) {
		fmt.Println("Didn't understand problem number", os.Args[2], "should be 1 or 2")
	}

	file, err := os.Open(filename)
	if err != nil {
		fmt.Println("Error opening file:", err)
		return
	}

	scanner := bufio.NewScanner(file)
	scanner.Split(bufio.ScanLines)
	workspace := new(Workspace)
	moves := []OperatorMove{}

	for scanner.Scan() {
		line := scanner.Text()

		if strings.Contains(line, "[") {
			fmt.Println("Adding workspace line")
			addLine(line, workspace)
		} else {
			move, err := parseMove(line)

			if err == nil {
				fmt.Println("Adding move", move)
				moves = append(moves, move)
			} else {
				fmt.Println("Skipping dead line")
			}
		}
	}

	file.Close()

	printWorkspace(*workspace)
	for count, move := range moves {
		fmt.Println("-----", count+1, "-----")
		runMove(problem, move, workspace)
		printWorkspace(*workspace)
	}

	resultString := ""
	for _, stack := range *workspace {
		if stack == nil {
			resultString += "*"
		} else {
			resultString += fmt.Sprintf("%c", rune((*stack).identity))
		}
	}
	fmt.Println("Final string is", resultString)
}