aoc-2022/day05/solution.go

package day05

import (
	"strconv"
	"strings"
)

type Solver struct {
	instructions []Instruction
	stacks       []Stack
}

type Instruction struct {
	count, from, to int
}

type Stack struct {
	containers []string
}

func (s *Stack) putAtBottom(container string) {
	s.containers = append([]string{container}, s.containers...)
}

func (s *Stack) putAtTop(container string) {
	s.containers = append(s.containers, container)
}

func (s *Stack) putNAtTop(containers []string) {
	s.containers = append(s.containers, containers...)
}

func (s *Stack) popFromTop() string {
	c := s.containers[len(s.containers)-1]
	s.containers = s.containers[:len(s.containers)-1]
	return c
}

func (s *Stack) popNFromTop(n int) []string {
	// a b c d; n == 2; len() = 4; indexes = len() - n, :
	c := s.containers[len(s.containers)-n:]
	s.containers = s.containers[:len(s.containers)-n]
	return c
}

func (s *Stack) peekTop() string {
	return s.containers[len(s.containers)-1]
}

func (s *Solver) ParseInput(input []string) {
	var containerList []string
	var instructionsLineIndex int

	for i, line := range input {
		if line == "" {
			instructionsLineIndex = i + 1
			break
		}
		containerList = append(containerList, line)
	}

	stackCountLine := []byte(containerList[len(containerList)-1])
	numStacks, _ := strconv.Atoi(string(stackCountLine[len(stackCountLine)-2]))

	s.stacks = make([]Stack, numStacks)

	for i := 0; i < len(containerList)-1; i++ {
		for _s := 0; _s < numStacks; _s += 1 {
			// 0 -> 1; 1 -> 5; 2 -> 9
			c := string([]byte(containerList[i])[4*_s+1])
			if c != " " {
				s.stacks[_s].putAtBottom(c)
			}
		}
	}

	for _, line := range input[instructionsLineIndex:] {
		tokens := strings.Split(line, " ")
		count, _ := strconv.Atoi(tokens[1])
		from, _ := strconv.Atoi(tokens[3])
		to, _ := strconv.Atoi(tokens[5])
		s.instructions = append(s.instructions, Instruction{count, from, to})
	}
}

func (s *Solver) SolvePart1() any {
	for _, instr := range s.instructions {
		for c := 0; c < instr.count; c += 1 {
			x := s.stacks[instr.from-1].popFromTop()
			s.stacks[instr.to-1].putAtTop(x)
		}
	}

	var r string
	for _, s := range s.stacks {
		r += s.peekTop()
	}
	return r
}

func (s *Solver) SolvePart2() any {
	for _, instr := range s.instructions {
		x := s.stacks[instr.from-1].popNFromTop(instr.count)
		s.stacks[instr.to-1].putNAtTop(x)
	}

	var r string
	for _, s := range s.stacks {
		r += s.peekTop()
	}
	return r
}