A* and HPA*

1. http://en.wikipedia.org/wiki/A*_search_algorithm, 
2. http://www.policyalmanac.org/games/aStarTutorial.htm, 
1. http://www.gamasutra.com/features/20010314/pinter_01.htm,
   
2. http://www.policyalmanac.org/games/binaryHeaps.htm, 
3. http://www.gamasutra.com/features/gdcarchive/2000/pottinger.doc,
   
4. ...
   
3. http://www.geocities.com/jheyesjones/astar.html, 
4. http://theory.stanford.edu/~amitp/GameProgramming/,
   
5. http://www.gamasutra.com/features/19970801/pathfinding.htm, 

HPA* Theory and Research:

• http://aigamedev.com/theory/near-optimal-hierarchical-pathfinding, 
• http://www.cs.ualberta.ca/~mmueller/ps/hpastar.pdf, 

Abstractions needed for implementation

• choice of heuristic 4 (admissible + not admissible, see 1.4 impl **)
  
• structure of node, extra nodes for current search, 1.4 (map./road)
  

• open / closed set storage 1.1, 1.2,
  
• Linked list
• Heap, 1.2,
• Matrix, 1.3
• preprocess inacessible areas / islands / dead ends
• variations, depth-first iterative deepening(lanctot-06-path-finding), IDA*(lanctot-06-path-finding), ..
  
• tie breakers, 1.4 (heuristics)
• early exit, 1.4 (impl.)
• resume / interrupt  + state, 1.4 (impl.)
• reuse last open / closed (e.g for other units), 1.4 (impl.)
• hierarchical, 1.4 (Maps)
  
• take from http://theory.stanford.edu/~amitp/GameProgramming/ImplementationNotes.html#S1
• path storage / compression, 1.4 (space)
  

Good Demo heuristic tests:

• search algortihms: http://www.gamasutra.com/features/19970801/pathfinding.htm

• heuristic compare: http://theory.stanford.edu/~amitp/GameProgramming/Heuristics.html