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V 6.1 Lightning-Fast ALT Bidirectional Pathfinding

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Downloads: 49
Change Set: 25973
Released: Jul 7, 2013
Updated: Jul 8, 2013 by pgeerkens
Dev status: Stable Help Icon

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Release Notes

  1. Upgraded to Visual Studio 2012
  2. Added BidirectionalPathfinder class (using ALT) that runs 240 times faster than previous using:
    • A (serial) implementation of New Parallel Bidirectional A*;
    • Heap-on-Top priority queue implementation;
    • A 32x32 BlockedBoardStorage class that improves caching of board details;
    • Implementation of ALT (A* with Landmarks and Triangle-inequality heuristic); and
    • A few scattered miscellaneous code improvements
  3. Additional basic functionality pushed into the HexBoard utility class from the examples, including the BoardStorage. abstraction discussed above.

This faster A* implementation decreases the time for my most complex case (two long diagonals on a 750 x 420 terrain map) from 860 ms and 1,550 ms to under 5 ms. Total nodes expanded decreases from 160,000 and 230,000 respectively to 1,600, of over 330,000 on the whole board.

Preprocessing of 8 landmarks (4 corners and the midpoints of all 4 sides) runs in about 4 seconds in parallel on an i7 using a simple Dijkstra's implementation, for a 760 x 420 terrain map.

The two cases are the same path in opposite directions, so the Bidirectional implementation now merges them to the same test case.

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