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// Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Rosetta Code-inspired maze generator and solver.
// Demonstrates use of interfaces to separate algorithm
// implementations (graph.ShortestPath, heap.*) from data.
// (In contrast, multiple inheritance approaches require
// you to store their data in your data structures as part
// of the inheritance.)
package main
import (
"bytes"
"fmt"
"math/rand"
"time"
"github.com/mattermost/rsc/rosetta/graph"
)
type Maze struct {
w, h int
grid [][]walls
}
type Dir uint
const (
North Dir = iota
East
West
South
)
type walls uint8
const allWalls walls = 1<<North | 1<<East | 1<<South | 1<<West
var dirs = []struct {
δx, δy int
}{
{0, -1},
{1, 0},
{-1, 0},
{0, 1},
}
// move returns the cell in the direction dir from position r, c.
// It returns ok==false if there is no cell in that direction.
func (m *Maze) move(x, y int, dir Dir) (nx, ny int, ok bool) {
nx = x + dirs[dir].δx
ny = y + dirs[dir].δy
ok = 0 <= nx && nx < m.w && 0 <= ny && ny < m.h
return
}
// Move returns the cell in the direction dir from position x, y
// It returns ok==false if there is no cell in that direction
// or if a wall blocks movement in that direction.
func (m *Maze) Move(x, y int, dir Dir) (nx, ny int, ok bool) {
nx, ny, ok = m.move(x, y, dir)
ok = ok && m.grid[y][x]&(1<<dir) == 0
return
}
// NewMaze returns a new, randomly generated maze
// of width w and height h.
func NewMaze(w, h int) *Maze {
// Allocate one slice for the whole 2-d cell grid and break up into rows.
all := make([]walls, w*h)
for i := range all {
all[i] = allWalls
}
m := &Maze{w: w, h: h, grid: make([][]walls, h)}
for i := range m.grid {
m.grid[i], all = all[:w], all[w:]
}
// All cells start with all walls.
m.generate(rand.Intn(w), rand.Intn(h))
return m
}
func (m *Maze) generate(x, y int) {
i := rand.Intn(4)
for j := 0; j < 4; j++ {
dir := Dir(i+j) % 4
if nx, ny, ok := m.move(x, y, dir); ok && m.grid[ny][nx] == allWalls {
// break down wall
m.grid[y][x] &^= 1 << dir
m.grid[ny][nx] &^= 1 << (3 - dir)
m.generate(nx, ny)
}
}
}
// String returns a multi-line string representation of the maze.
func (m *Maze) String() string {
return m.PathString(nil)
}
// PathString returns the multi-line string representation of the
// maze with the path marked on it.
func (m *Maze) PathString(path []graph.Vertex) string {
var b bytes.Buffer
wall := func(w, m walls, ch byte) {
if w&m != 0 {
b.WriteByte(ch)
} else {
b.WriteByte(' ')
}
}
for _, row := range m.grid {
b.WriteByte('+')
for _, cell := range row {
wall(cell, 1<<North, '-')
b.WriteByte('+')
}
b.WriteString("\n")
for _, cell := range row {
wall(cell, 1<<West, '|')
b.WriteByte(' ')
}
b.WriteString("|\n")
}
for i := 0; i < m.w; i++ {
b.WriteString("++")
}
b.WriteString("+")
grid := b.Bytes()
// Overlay path.
last := -1
for _, v := range path {
p := v.(pos)
i := (2*m.w+2)*(2*p.y+1) + 2*p.x + 1
grid[i] = '#'
if last != -1 {
grid[(i+last)/2] = '#'
}
last = i
}
return string(grid)
}
// Implement graph.Graph.
type pos struct {
x, y int
}
func (p pos) String() string {
return fmt.Sprintf("%d,%d", p.x, p.y)
}
func (m *Maze) Neighbors(v graph.Vertex) []graph.Vertex {
p := v.(pos)
var neighbors []graph.Vertex
for dir := North; dir <= South; dir++ {
if nx, ny, ok := m.Move(p.x, p.y, dir); ok {
neighbors = append(neighbors, pos{nx, ny})
}
}
return neighbors
}
func (m *Maze) NumVertex() int {
return m.w * m.h
}
func (m *Maze) VertexID(v graph.Vertex) int {
p := v.(pos)
return p.y*m.w + p.x
}
func (m *Maze) Vertex(x, y int) graph.Vertex {
return pos{x, y}
}
func main() {
const w, h = 30, 10
rand.Seed(time.Now().UnixNano())
m := NewMaze(w, h)
path := graph.ShortestPath(m, m.Vertex(0, 0), m.Vertex(w-1, h-1))
fmt.Println(m.PathString(path))
}
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