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A puzzle is a problem or enigma presented as entertainment; that is written down, acted out, etc. Many puzzles stem from serious mathematical or logistical problems, whereas others are devised for the sole purpose of being brain teasers. The history of puzzles goes back many thousand years, a tangram being one of the earliest and still one of the most popular puzzles. In certain temples of Japan monks used to write mathematical puzzles on temple walls: see sangaku.
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A maze is a tour puzzle in the form of a complex branching passage through which the solver must find a route. This is different from a labyrinth, which has an unambiguous through-route and is not designed to be difficult to navigate.
The pathways and walls in a maze or labyrinth are fixed. Maze-type puzzles where the given walls and paths may change during the game are covered under the main puzzle category of tour puzzles.
One type of maze consists of a set of rooms linked by doors (so a passageway is just another room in this definition). You enter at one spot, and exit at another, or the idea may be to reach a certain spot in the maze.
Mazes have been built with walls and rooms, with hedges, turf, or crops such as corn or, indeed, maize, or with paving stones of contrasting colors or designs.
Mazes can also be drawn on paper to be followed by a pencil.
One of the short stories of Jorge Luis Borges featured a book that was a literary maze.
Various maze generation algorithms exist for building mazes, either by hand or by computer.
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The mathematician Leonhard Euler was one of the first to analyse plane mazes mathematically, and in doing so founded the science of topology.
The following algorithms are designed to be used inside the maze by a traveler with no prior knowledge of the maze's layout. There are other algorithms that can be used for solving paper mazes, where the solver has an overview of the maze.
The wall follower, the best-known rule for traversing mazes, is also known as either the left-hand rule or the right-hand rule. If the maze is simply connected, that is, all its walls are connected together or to the maze's outer boundary, by keeping one hand in contact with one wall of the maze you are guaranteed not to get lost and will reach a different exit if there is one; otherwise, you will return to your entrance. If the maze is not simply connected, this method will not help you to find the disjoint parts of the maze.
Wall following can be done in 3D or higher dimensional mazes if you project its higher dimensional passages onto the 2D plane in a deterministic manner. For example, in a 3D maze pretend up passages actually lead northwest, and down passages actually lead southeast, and then apply the standard wall following rules.
Disjoint mazes can still be solved with the wall follower method, if the entrance and exit to the maze are on the outer walls of the maze. If however, the solver starts inside the maze, it might be on a section disjoint from the exit, and wall followers will continually go around their ring. The Pledge algorithm (named after Jon Pledge of Exeter) can solve this problem.
The Pledge algorithm, designed to circumvent obstacles, requires an arbitrarily chosen direction to go towards. When an obstacle is met, one hand (say the right hand) is kept along the obstacle while the angles turned are counted. When the solver is facing the original direction again, and the angular sum of the turns made is 0, the solver leaves the obstacle and continues moving in its original direction.
This algorithm allows a person with a compass to find their way from any point inside to an outer exit of any finite and fair 2 dimensional maze, regardless of the initial position of the solver. However, this algorithm will not work in doing the reverse, namely finding your way from an entrance on the outside of a maze to some end goal within it.
This is a trivial method that can be implemented by a very unintelligent robot or perhaps a mouse, but which is not guaranteed to work. It is simply to proceed in a straight line until an obstruction is reached, and then to make a random decision about the next direction to follow. This will of course fail if the exit is, or is only reachable by, an opening in the middle of a wall.
Tremaux's algorithm is an efficient method that requires drawing a line on the floor to mark your path, and is guaranteed to work for all mazes that have well-defined passages. On arriving at an unmarked junction, pick any direction. If you have visited the junction before, return the way you came. If revisiting a passage that is already marked, draw a second line, and at the next junction, take any unmarked passage if possible, otherwise take a marked one. You will never need to take any passage more than twice. If there is no exit, this method will take you back to the start.
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There are many different approaches to automate the generation of mazes.
This is also the most simple way to generate a maze using a computer. Consider the space for a maze being a large grid of cells (like a large chess board), and each cell starts with 4 walls. Pick a random start cell and then select a random neighbouring cell that has not yet been visited. Remove the 'wall' between the two cells and add the new cell to a stack (this is analogous to drawing the line on the floor). Continue this process, if you ever get to a cell that has no unvisited neighbours then you have come to a dead-end. When at a dead-end backtrack through your path (pop from the stack) until you get to a cell with an unvisited neighbour, continue your path generation by visiting this new, unvisited cell (creating a new junction). This process continues until you have visited every cell, causing you to backtrack all the way back to the begining cell. This approach gaurantees that the maze space is completely visited. As stated, the algorithm is very simple and does not produce overly complex mazes. More specific refinements to the algorithm can help to generate harder to solve mazes.
Maze (Henry Holt & Company, Inc.; (February 1989), ISBN 0805010882), billed as "The World's Hardest Puzzle", is a 45-room house in the form of a book. A party of naïve adventurers is led through by an unnamed poet/architect, whose identity is a subject of much speculation. Each page is a room, with hundreds of possible visual clues in the picture along with the numbers of the rooms that can be entered, and a page describing the actions of the narrator and the adventurers which may contain even more clues. The object is to reach the "center" (Page 45), answer the riddle found there, and get back out in the fewest possible steps (16).
Mazes are often used in science experiments to study spatial navigation and learning. Such experiments typically use rats or mice. Examples are