LeetCode/go/regions-cut-by-slashes.go

package main

import aq "github.com/emirpasic/gods/v2/queues/arrayqueue"

type Position struct {
	y, x int
}

const (
	WALL  int = -1
	BLANK int = 0
	SEEN  int = 1
)

func regionsBySlashes(grid []string) int {
	POSITIONS := []Position{
		Position{0, 1},
		Position{0, -1},
		Position{1, 0},
		Position{-1, 0},
	}

	n := len(grid)

	makeGraph := func() [][]int {
		graph := make([][]int, 3*n)
		for i := range graph {
			graph[i] = make([]int, 3*n)
		}

		for y0, row := range grid {
			for x0, cell := range row {
				y, x := 3*y0, 3*x0

				if cell == '/' {
					graph[y][x+2] = WALL
					graph[y+1][x+1] = WALL
					graph[y+2][x] = WALL
				} else if cell == '\\' {
					graph[y][x] = WALL
					graph[y+1][x+1] = WALL
					graph[y+2][x+2] = WALL
				}
			}
		}

		return graph
	}

	visit := func(g [][]int, p Position) bool {
		return p.y >= 0 && p.y < len(g) && p.x >= 0 && p.x < len(g[p.y]) && g[p.y][p.x] == BLANK
	}

	fill := func(g [][]int, y, x int) {
		q := aq.New[Position]()
		q.Enqueue(Position{y, x})

		for p, ok := q.Dequeue(); ok; p, ok = q.Dequeue() {
			for _, d := range POSITIONS {
				next := Position{p.y + d.y, p.x + d.x}

				if visit(g, next) {
					q.Enqueue(next)
					g[next.y][next.x] = SEEN
				}
			}
		}
	}

	graph := makeGraph()

	regions := 0
	for p := 0; p < 9*n*n; p++ {
		y, x := p/(3*n), p%(3*n)

		if graph[y][x] == BLANK {
			fill(graph, y, x)
			regions++
		}
	}

	return regions
}