Maze Router Applet - A* Algorithm
This applet demonstrates a variation on Maze Routing that
reduces the execution time compared to the Lee Algorithm. About the A* AlgorithmThe A* Algorithm is a variation on the Lee Algorithm that reduces execution time during the expansion phase by biasing the search in the direction of the target. Unlike the Lee Algorithm, which uses the distance from the source as its cost function, Hadlock's algorithm uses a value known as a cost f
= g + h
where g is the distance of a
labelled grid from the source (i.e., the cost used in the Lee
algorithm), and h is a an
estimate of the cost from the labeled gridpoint to the target (i.e.,
the Manhattan distance from the gridpoint to the target). Thus
nodes which are closer to the target have lower costs than nodes that
are further from the target. Since the expansion algorithm
selects nodes with the lowest
cost for expansion, this biases the search in the direction of the
target. When an obstacle is reached, a detour is necessary and
nodes labeled with higher values are expanded. The backtrace
phase operates identically to the Lee Algorithm.Because it still does exhaustive search as a fallback, the A* algorithm still guarantees that a minimum-cost connection will be found if it exists. References F. Rubin, "The Lee path connection algorithm", IEEE Transactions on Computers, Vol. C-23, 1974, pp 907 - 914. Wikipedia, "A* search algorithm", February 2007. |

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Last updated on January 25, 2007 by John A. Nestor