aoc2023/day10/day10.go

package day10

import (
	"fmt"
	"log"
)

const (
	EAST  = 'E'
	SOUTH = 'S'
	WEST  = 'W'
	NORTH = 'N'
)

type Move struct {
	row    int
	col    int
	origin rune
	count  int
}

//var checked = map[Move]bool{}

func findStart(lines []string) (*Move, *Move, *Move) {

	var start *Move

OuterLoop:
	for row, l := range lines {
		for col, c := range l {
			if c == 'S' {
				start = &Move{row, col, 0, 0}

				break OuterLoop
			}
		}
	}

	m := make([]*Move, 2)
	i := 0

	if start.row >= 1 && (lines[start.row-1][start.col] == '7' || lines[start.row-1][start.col] == '|' || lines[start.row-1][start.col] == 'F') {
		m[i] = &Move{start.row - 1, start.col, 'S', 1}
		i++
	}

	if start.row <= len(lines)-2 && (lines[start.row+1][start.col] == 'L' || lines[start.row+1][start.col] == '|' || lines[start.row+1][start.col] == 'J') {
		m[i] = &Move{start.row + 1, start.col, 'N', 1}
		i++
	}

	if start.col >= 1 && (lines[start.row][start.col-1] == '-' || lines[start.row][start.col-1] == 'L' || lines[start.row][start.col-1] == 'F') {
		m[i] = &Move{start.row, start.col - 1, 'E', 1}
		i++
	}

	width := len(lines[start.row])
	if start.col <= width-2 && (lines[start.row][start.col+1] == '-' || lines[start.row][start.col+1] == 'J' || lines[start.row][start.col+1] == '7') {
		m[i] = &Move{start.row, start.col + 1, 'W', 1}
		i++
	}

	return start, m[0], m[1]
}

func nextMove(m *Move, lines []string) *Move {
	switch lines[m.row][m.col] {
	case '|': // vertical pipe connecting north and south.
		if m.origin == 'N' {
			return &Move{m.row + 1, m.col, 'N', m.count + 1}
		} else {
			return &Move{m.row - 1, m.col, 'S', m.count + 1}
		}
	case '-': // horizontal pipe connecting east and west.
		if m.origin == 'W' {
			return &Move{m.row, m.col + 1, 'W', m.count + 1}
		} else {
			return &Move{m.row, m.col - 1, 'E', m.count + 1}
		}
	case 'L': // 90-degree bend connecting north and east.
		if m.origin == 'N' {
			return &Move{m.row, m.col + 1, 'W', m.count + 1}
		} else {
			return &Move{m.row - 1, m.col, 'S', m.count + 1}
		}
	case 'J': // 90-degree bend connecting north and west.
		if m.origin == 'N' {
			return &Move{m.row, m.col - 1, 'E', m.count + 1}
		} else {
			return &Move{m.row - 1, m.col, 'S', m.count + 1}
		}
	case '7': // 90-degree bend connecting south and west.
		if m.origin == 'S' {
			return &Move{m.row, m.col - 1, 'E', m.count + 1}
		} else {
			return &Move{m.row + 1, m.col, 'N', m.count + 1}
		}
	case 'F': // a 90-degree bend connecting south and east.
		if m.origin == 'S' {
			return &Move{m.row, m.col + 1, 'W', m.count + 1}
		} else {
			return &Move{m.row + 1, m.col, 'N', m.count + 1}
		}
	case 'S': // is ground; there is no pipe in this tile.
		return m
	case '.': // is ground; there is no pipe in this tile.
		log.Fatalf("Should not find ground %v : ", m)
	default:
		log.Fatalf("Impossible move %v : ", m)
	}

	return nil
}

func FindDistance(lines []string) int {

	/*
				Iterative DFS
				-------------

		    let S be a stack
		    S.push(v)
		    while S is not empty do
		        v = S.pop()
		        if v is not labeled as discovered then
		            label v as discovered
		            for all edges from v to w in G.adjacentEdges(v) do
		                S.push(w)

		stack := utils.NewStack[*Move](140 * 140)
		stack.Push(findStart(lines))

		for stack.HasElement() {
			lastMove := stack.Pop()
		}
	*/

	start, m1, m2 := findStart(lines)
	fmt.Println("Starting at ", *start)

	for {
		if m1.col == m2.col && m1.row == m2.row {
			fmt.Println("Finished at ", *m1)
			return m1.count
		} else {
			m1 = nextMove(m1, lines)
			m2 = nextMove(m2, lines)
		}
	}
}

// Point in Polygon algorithm
func isInPolygon(row int, col int, lines [][]rune) bool {
	count := 0
	last := rune(0)
	for i := col; i < len(lines[row]); i++ {
		c := lines[row][i]
		switch c {
		case 'S', '|', 'L', 'J', '7', 'F': // skip '-' and do not count it as part of the polygon border
			if last == 'F' && c == 'J' || last == 'L' && c == '7' { // count these as a single border of the polygon
				last = c
				continue
			}
			last = c
			count++
		}

	}
	return count%2 == 1
}

func CountInPolygon(lines []string) int {
	writeableLines := make([][]rune, len(lines))

	for i := range lines {
		writeableLines[i] = []rune(lines[i])
	}

	// delimit the loop with a specific rune different from the ones used in the problem ('*')
	start, m1, m2 := findStart(lines)
	fmt.Println("Starting at ", *start)
	writeableLines[start.row][start.col] = '*'
	writeableLines[m1.row][m1.col] = '*'
	writeableLines[m2.row][m2.col] = '*'

	for {
		if m1.col == m2.col && m1.row == m2.row {
			fmt.Println("Finished at ", *m1)
			break
		} else {
			m1 = nextMove(m1, lines)
			m2 = nextMove(m2, lines)
			writeableLines[m1.row][m1.col] = '*'
			writeableLines[m2.row][m2.col] = '*'
		}
	}

	// mark all tile that are not part of the loop as a tile that can count in the total with rune '.'
	for row, l := range writeableLines {
		for col, c := range l {
			if c != '*' {
				writeableLines[row][col] = '.'
			}
		}
	}

	// reproduce the original loop in the grid with the '.' correctly set up
	for row, l := range writeableLines {
		for col, c := range l {
			if c == '*' {
				writeableLines[row][col] = []rune(lines[row])[col]
			}
		}
	}

	result := 0

	for row, l := range writeableLines {
		for col, c := range l {
			if c == '.' {
				if isInPolygon(row, col, writeableLines) {
					result++
				}
			}
		}
	}

	return result
}