From e8bb5d909aa47e0f5698ad5f842386aa1b671dc0 Mon Sep 17 00:00:00 2001
From: Matej Focko <me@mfocko.xyz>
Date: Sat, 10 Aug 2024 11:13:11 +0200
Subject: [PATCH] =?UTF-8?q?go:=20add=20=C2=AB959.=20Regions=20Cut=20By=20S?=
 =?UTF-8?q?lashes=C2=BB?=
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Signed-off-by: Matej Focko <me@mfocko.xyz>
---
 go/regions-cut-by-slashes.go | 83 ++++++++++++++++++++++++++++++++++++
 1 file changed, 83 insertions(+)
 create mode 100644 go/regions-cut-by-slashes.go

diff --git a/go/regions-cut-by-slashes.go b/go/regions-cut-by-slashes.go
new file mode 100644
index 0000000..a69fbc7
--- /dev/null
+++ b/go/regions-cut-by-slashes.go
@@ -0,0 +1,83 @@
+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
+}