Advent-of-Code-2023/day14/dayFourteen.go

package day14

import (
	"fmt"
	"log"
	"os"
	"strings"
)

func Run() int {
	fmt.Println("hello day 14")

	field := ReadPlatform("day14/input")
	fmt.Println(field.String())

	// fmt.Printf("> lines for field %+v\n", field.UpIndices())
	// field.Move(field.Height(), field.UpIndices())
	cycles := 1000000000
	states := make(map[string]int)
	// 2023/12/14 11:50:32 >>> found loop. known state after 10 equal to one after 3

	var loopLen, initialStretch int

	for i := 1; i <= cycles; i++ {
		field.DoSpinCycle()
		// fmt.Println(field.String())

		stringRepr := field.String()
		prevIter, known := states[stringRepr]
		if known {
			log.Printf(">>> found loop. known state after %d equal to one after %d", i, prevIter)
			initialStretch = prevIter
			loopLen = i - prevIter
			break
		}

		states[stringRepr] = i

		if i % 100000 == 0 {
			log.Print("done ", i, " cycles")
		}
	}

	// field is already in a 'loop' state.
	// so we've already done 'initial stretch' so to make field in same state as after 'cycles'
	// i only need to check rest of (cycles - initialStretch)
	movesToMake := (cycles - initialStretch)%loopLen
	log.Printf(">>> data: initial steps %d, loop len %d. to do same as %d iterations i need %d", initialStretch, loopLen, cycles, movesToMake)

	for i := 1; i <= movesToMake; i++ {
		field.DoSpinCycle()
		// fmt.Println(field.String())
	}

	// north rock load
	return field.NorthLoad()
}

const Rock rune = 'O'
const Wall rune = '#'
const Space rune = '.'

type Platform struct {
	Rocks [][]rune
}

func (p *Platform) Height() int {
	return len(p.Rocks)
}
func (p *Platform) Width() int {
	return len(p.Rocks[0])
}

func ReadPlatform(filename string) Platform {
	bytes, err := os.ReadFile(filename)
	if err != nil {
		panic(fmt.Sprint("cannot read file: ", filename))
	}
	text := string(bytes)
	text = strings.TrimSpace(text)
	lines := strings.Split(text, "\n")

	rocks := make([][]rune, len(lines))
	for i, line := range lines {
		rocks[i] = []rune(line)
	}

	return Platform{
		Rocks: rocks,
	}
}

func (p *Platform) String() string {
	text := "\n"
	for _, row := range p.Rocks {
		text += string(row)
		text += "\n"
	}

	return text
}

type Coord struct{ Row, Col int }

// indices for moving UP, from down to up
func (p *Platform) UpIndices() [][]Coord {
	lines := make([][]Coord, 0)
	for col := 0; col < p.Width(); col++ {
		line := make([]Coord, 0)
		for row := 0; row < p.Height(); row++ {
			line = append(line, Coord{Row: row, Col: col})
		}
		lines = append(lines, line)
	}
	return lines
}

// indices for moving DOWN, from up to down
func (p *Platform) DownIndices() [][]Coord {
	lines := make([][]Coord, 0)
	for col := 0; col < p.Width(); col++ {
		line := make([]Coord, 0)
		for row := p.Height() - 1; row >= 0; row-- {
			line = append(line, Coord{Row: row, Col: col})
		}
		lines = append(lines, line)
	}
	return lines
}

// indices for moving RIGHT from right to left
func (p *Platform) RightIndices() [][]Coord {
	lines := make([][]Coord, 0)
	for row := 0; row < p.Height(); row++ {
		line := make([]Coord, 0)
		for col := p.Width() - 1; col >= 0; col-- {
			line = append(line, Coord{Row: row, Col: col})
		}
		lines = append(lines, line)
	}
	return lines
}

// indices for moving LEFT, from left to right
func (p *Platform) LeftIndices() [][]Coord {
	lines := make([][]Coord, 0)
	for row := 0; row < p.Height(); row++ {
		line := make([]Coord, 0)
		for col := 0; col < p.Width(); col++ {
			line = append(line, Coord{Row: row, Col: col})
		}
		lines = append(lines, line)
	}
	return lines
}

func (p *Platform) SymbAt(coord Coord) rune {
	return p.Rocks[coord.Row][coord.Col]
}
func (p *Platform) SetSymbAt(coord Coord, symb rune) {
	p.Rocks[coord.Row][coord.Col] = symb
}

func (p *Platform) Move(n int, lines [][]Coord) {
	for _, line := range lines {
		moveSize := 0
		for i, coord := range line {
			symb := p.SymbAt(coord)
			switch symb {
			case Space:
				moveSize += 1
				if moveSize > n {
					moveSize = n
				}
			case Wall:
				moveSize = 0
			case Rock:
				if moveSize == 0 {
					continue
				}
				// get coord for moveSize back. and set that to 'o'
				// and set current to '.'
				// panic if that place is not '.' i guess
				moveTo := line[i-moveSize]
				symbAtTarget := p.SymbAt(moveTo)
				if symbAtTarget != Space {
					panic(fmt.Sprintf("attempting to move %+v to %+v, target symbol is %s, not '.'",
						coord, moveTo, string(symbAtTarget)))
				}
				p.SetSymbAt(moveTo, Rock)
				p.SetSymbAt(coord, Space)
			}
		}
	}
}

func (p *Platform) NorthLoad() int {
	total := 0
	height := p.Height()
	for i, row := range p.Rocks {
		for _, symb := range row {
			if symb == Rock {
				total += (height - i)
			}
		}
	}
	return total
}

func (p *Platform) DoSpinCycle() {
	// north, west, south, east - till the end
	p.Move(p.Height(), p.UpIndices())
	p.Move(p.Width(), p.LeftIndices())
	p.Move(p.Height(), p.DownIndices())
	p.Move(p.Width(), p.RightIndices())
}