A PHP maze generator

maze.php

<?php
/**
 * Maze.php
 *
 * Based on: https://github.com/chimericdream/PHP-Maze-Generator/blob/master/Maze.php
 * This file contains the declaration for the Maze class.
 *
 * @file       Maze.php
 * @author     Bill Parrott <bparrott@ku.edu>
 * @date       11/30/2012
 * @version    1.0.0
 */

class Maze
{
	const DEFAULT_MAZE_HEIGHT = 15;
	const DEFAULT_MAZE_WIDTH  = 15;

	private $cells            = array();
	private $walls            = array();
	private $eqClasses        = array();
	private $remainingClasses = 0;
	private $x                = 0;
	private $y                = 0;
	private $cellCount        = 0;
	private $wallCount        = 0;

	private $icon_wall = array( '🌲', '🌳', '🌴', '🏔', '⛰', '💧', '🔥', '🚧', '🗿', '🌋' );
	private $icon_gap = array( '🟩', '🟨', '🟥', '🟫', '🟧', '⬜️' );
	private $icon_start = array( '😄', '🧟‍♂️', '👳‍♂️', '🧞‍♂️', '🏃‍♂️', '💃', '🦹‍♀️', '🧕', '👩‍🦰', '👸', '🐈' );
	private $icon_end = array( '🏠', '🏦', '🏩', '🏫', '🏡', '🚙', '🚕', '🏕', '⛺️', '🎪', '🏰', '✈️', '🚃', '🛖' );

	//RandomGen r;


	/**
	 * __construct()
	 *
	 * Class constructor. This sets the height and width of the maze then calls
	 * buildBaseMaze() to initialize the arrays.
	 *
	 * @param int x The width of the maze to generate; defaults to DEFAULT_MAZE_WIDTH
	 * @param int y The height of the maze to generate; defaults to DEFAULT_MAZE_HEIGHT
	 * @return n/a (Constructor)
	 */
	public function __construct($x = self::DEFAULT_MAZE_WIDTH, $y = self::DEFAULT_MAZE_HEIGHT)
	{
		$this->x = $x;
		$this->y = $y;

		$this->buildBaseMaze();
	} //end __construct


	/**
	 * generate()
	 *
	 * Magic! This method uses the union/find algorithm to determine whether
	 * two adjacent rooms are in the same set. If they are not, it performs
	 * a union by knocking out the wall between them. Once all cells in the
	 * maze are in the same set, the maze is complete and there exists a
	 * path from every cell in the maze to every other cell.
	 *
	 * @return void
	 */
	public function generate()
	{

		while ($this->disjointCellsExist()) {
			$c    = $this->getRandomCell();
			$wall = $this->getRandomInnerWall($c);
			$n    = $this->getNeighboringCell($c, $wall);

			if (!$this->checkConnected($c, $n)) {
				$this->removeWall($wall);
				$this->connect($c, $n);
			}
		}

	} //end generate


	/**
	 * display()
	 *
	 * Wrapper for the other print function that defaults to using std::cout
	 * as the output location.
	 *
	 * @return void
	 */
	public function render() {

		// Each row is 2 character lines high, including top border, then add 1 for
		// bottom border of the maze
		$printRows = (2 * $this->y) + 1;

		$currWall = 0;
		$currCell = 0;

		$html = '';

		$icon_start = $this->pick_icon( $this->icon_start );
		$icon_end = $this->pick_icon( $this->icon_end );
		$icon_wall = $this->pick_icon( $this->icon_wall );
		$icon_gap = $this->pick_icon( $this->icon_gap );

		// Loop through Rows.
		for ($i = 0; $i < $printRows; $i++) {

			// If a wall row then fill it out.
			if ( 0 === $i % 2 ) {

				// Printing a top border.
				for ( $j = 0; $j < $this->x; $j++ ) {

					// Top-left corner does not need top-left divider; needs a space
					// to line everything up, though.
					// Wall column.
					if ( $j > 0 || $i > 0 ) {
						$html .= $icon_wall;
					} else {
						$html .= $icon_start;
					}

					// Gap column.
					if ( $this->walls[$currWall++] == 1 ) {
						$html .= $icon_wall;
					} else {
						$html .= $icon_gap;
					}

				}

				// Bottom-right corner does not need bottom-right divider.
				if ( $i !== ( $printRows - 1 ) ) {
					$html .= $icon_wall;
				} else {
					$html .= $icon_end;
				}

			} else {

				// Printing the cell itself.
				for ( $j = 0; $j < $this->x; $j++ ) {
					if ( 1 === $this->walls[$currWall++] ) {
						$html .= $icon_wall;
					} else {
						$html .= $icon_gap;
					}

					$html .= $icon_gap;

				}

				// Print the right wall if needed.
				if ( 1 === $this->walls[$currWall++] ) {
					$html .= $icon_wall;
				} else {
					$html .= $icon_gap;
				}

			}
			$html .= "\r\n";

		}

		return $html;

	} //end display


	public function display() {

		echo $this->render();

	}


	private function pick_icon( $icons ) {

		shuffle( $icons );
		return $icons[0];

	}


	/**
	 * buildBaseMaze()
	 *
	 * Initializes the grid of cells/rooms in the maze. To start, all cells
	 * are in their own equivalence class. Also initializes all walls as
	 * visible. Finally, knock out the walls in the upper-left and
	 * bottom-right corners.
	 *
	 * @return void
	 */
	private function buildBaseMaze()
	{
		$this->cellCount        = $this->x * $this->y;
		$this->wallCount        = ($this->x * ($this->y + 1)) + ($this->y * ($this->x + 1));
		$this->remainingClasses = $this->cellCount;

		// Set all the walls to be on to start
		for ($i = 0; $i < $this->wallCount; $i++) {
			$this->walls[$i] = 1;
		}

		// Initialize the cells to be independent of one another
		for ($i = 0; $i < $this->cellCount; $i++) {
			$c = array(
				'idx'    => $i,
				'parent' => NULL,
			);
			$this->cells[$i]     = $c;
			$this->eqClasses[$i] = $i;
		}

		// Remove top-left corner walls
		$this->removeWall(0);
		$this->removeWall($this->x);

		// Remove bottom-right corner walls
		$this->removeWall($this->wallCount - ($this->x + 1));
		$this->removeWall($this->wallCount - 1);
	} //end buildBaseMaze


	/**
	 * checkConnected()
	 *
	 * The find portion of the union/find algorithm, this checks whether the
	 * specified cells have the same equivalence class (i.e. whether they)
	 * are connected within the maze.
	 *
	 * @return bool Whether two cells have the same equivalence class.
	 */
	private function checkConnected(array $c1, array $c2)
	{
		if ($this->eqClasses[$c1['idx']] == $this->eqClasses[$c2['idx']]) {
			return true;
		} else {
			return false;
		}
	} //end checkConnected


	/**
	 * connect()
	 *
	 * Using the union portion of the union/find algorithm, this method
	 * connects two cells/rooms in the maze. It gets the equivalence class
	 * of c1 and sets c2's parent to c1's root parent. It then sets the
	 * equivalence class of all cells that matched c2's old class to equal
	 * c1's equivalence class.
	 *
	 * @return void
	 */
	private function connect(array $c1, array $c2)
	{
		// The root parent of c1 is its equivalence class.
		$temp1 = $this->cells[$this->eqClasses[$c1['idx']]];
		$temp1['parent'] = $c2['idx'];

		$oldClass  = $this->eqClasses[$temp1['idx']];
		$newClass  = $this->eqClasses[$c2['idx']];

		for ($i = 0; $i < $this->cellCount; $i++) {
			if ($this->eqClasses[$i] == $oldClass) {
				$this->eqClasses[$i] = $newClass;
			}
		}

		$this->remainingClasses--;
	} //end connect


	/**
	 * removeWall()
	 *
	 * Set the specified wall to invisible.
	 *
	 * @return void
	 */
	private function removeWall($idx)
	{
		$this->walls[$idx] = 0;
	} //end removeWall


	/**
	 * getRandomCell()
	 *
	 * Pick a cell at random within the maze. This is the first step during
	 * the generation process.
	 *
	 * @return Cell* A random cell in the maze.
	 */
	private function getRandomCell()
	{
		$idx = rand(0, $this->cellCount - 1);
		return $this->cells[$idx];
	} //end getRandomCell


	/**
	 * getRandomInnerWall()
	 *
	 * Given a particular cell/room in the maze, pick one of its inner walls
	 * at random. An inner wall is one that is adjacent to another cell/room
	 * in the maze and not part of the outer border of the overall grid.
	 *
	 * @return int The index of a random inner wall adjacent to the room.
	 */
	private function getRandomInnerWall(array $c)
	{
		$n = $s = $e = $w = true;
		if ($c['idx'] < $this->x) {
			$n = false;
		}
		if ($c['idx'] >= ($this->cellCount - $this->x)) {
			$s = false;
		}
		if ($c['idx'] % $this->x == ($this->x - 1)) {
			$e = false;
		}
		if ($c['idx'] % $this->x == 0) {
			$w = false;
		}

		// Determine which row the cell is in
		$row = floor($c['idx'] / $this->x);

		// Wall indexes for the north, west, east, and south
		$nx = $c['idx'] + ($row * $this->x) + $row;
		$wx = $nx + $this->x;
		$ex = $nx + $this->x + 1;
		$sx = $nx + (2 * $this->x) + 1;

		while (true) {
			$wall = rand(1,4);
			switch ($wall) {
				case 1:
					if ($n === true) {
						return $nx;
					}
					break;
				case 2:
					if ($w === true) {
						return $wx;
					}
					break;
				case 3:
					if ($e === true) {
						return $ex;
					}
					break;
				case 4:
					if ($s === true) {
						return $sx;
					}
					break;
			}
		}
	} //end getRandomInnerWall


	/**
	 * getNeighboringCell()
	 *
	 * Given a cell and a wall, this method determines which room is on the
	 * other side of said wall.
	 *
	 * @return Cell* Returns a pointer to the cell on the other side of the
	 *               wall.
	 */
	private function getNeighboringCell(array $c, $wall)
	{
		// Determine which row the cell is in
		$row = floor($c['idx'] / $this->x);

		// Wall indexes for the north, west, east, and south
		$n = $c['idx'] + ($row * $this->x) + $row;
		$w = $n + $this->x;
		$e = $n + $this->x + 1;
		$s = $n + (2 * $this->x) + 1;

		// Indexes for the cells to the north, west, east, and south
		$nx = $c['idx'] - $this->x;
		$wx = $c['idx'] - 1;
		$ex = $c['idx'] + 1;
		$sx = $c['idx'] + $this->x;

		if ($wall == $n) {
			return $this->cells[$nx];
		}
		if ($wall == $w) {
			return $this->cells[$wx];
		}
		if ($wall == $e) {
			return $this->cells[$ex];
		}
		if ($wall == $s) {
			return $this->cells[$sx];
		}
	} //end getNeighboringCell


	/**
	 * disjointCellsExist()
	 *
	 * This method checks how many equivalence classes remain. The number of
	 * equivalence classes represents how many disjoint sets of cells there
	 * are. Initially it is equal to the number of cells in the maze. Each
	 * time a wall is knocked out, two sets become connected, so the total
	 * number of disjoint sets is reduced by one. Once the number of sets
	 * reaches 1, it means that all cells in the maze are connected to all
	 * other cells by at least one path.
	 *
	 * @return bool Whether any disjoint cells still exist
	 */
	private function disjointCellsExist()
	{
		if ($this->remainingClasses > 1) {
			return true;
		}

		return false;
	} //end disjointCellsExist
} //end class Maze