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Basic Search Procedure

The search procedure involves starting with the root node, expanding nodes based on search strategies, and finding the goal node. Different search strategies like Breadth-First and Depth-First are used in problem-solving tasks.

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Basic Search Procedure

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  1. Basic Search Procedure • 1. Start with the start node (root of the search tree) and place in on the queue • 2. Remove the front node in the queue and • If the node is a goal node, then we are done; stop. • Otherwise expand the node  generate its children using the successor function (other states that can be reached with one move) • 3. Place the children on the queue according to the search strategy • 4. Go back to step 2.

  2. Search Strategies • Search strategies differ based on the order in which new successor nodes are added to the queue • Breadth-first  add nodes to the end of the queue • Depth-first  add nodes to the front • Uniform cost  sort the nodes on the queue based on the cost of reaching the node from start node

  3. Breadth-First Searchadd nodes to the end of the queue

  4. Breadth-First Search A B I E C D M K F H N O G Q R T goal P S Queue:  A

  5. Breadth-First Search A B I E C D M K F H N O G Q R T goal P S Queue:  B I E

  6. Breadth-First Search A B I E C D M K F H N O G Q R T goal P S Queue:  I E C D

  7. Breadth-First Search A B I E C D M K F H N O G Q R T goal P S Queue:  E C D M K

  8. Breadth-First Search A B I E C D M K F H N O G Q R T goal P S Queue:  C D M K F H

  9. Breadth-First Search A B I E C D M K F H N O G Q R T goal P S Queue:  D M K F H N

  10. Breadth-First Search A B I E C D M K F H N O G Q R T goal P S Queue:  M K F H N

  11. Breadth-First Search A B I E C D M K F H N O G Q R T goal P S Queue:  K F H N O G

  12. Breadth-First Search A B I E C D M K F H N O G Q R T goal P S Queue:  F H N O G

  13. Breadth-First Search A B I E C D M K F H N O G Q R T goal P S Queue:  H N O G Q

  14. Breadth-First Search A B I E C D M K F H N O G Q R T goal P S Queue:  N O G Q R T

  15. Breadth-First Search A B I E C D M K F H N O G Q R T goal P S Queue:  O G Q R T P S

  16. Breadth-First Search A B I E C D M K F H N O G Q R T goal P S Queue:  G Q R T P S

  17. Breadth-First Search A B I E C D M K F H N O G Q R T goal P S DONE!!! Solution: A  I  M  G Queue:  Q R T P S

  18. Depth-First Searchadd nodes to the front of the queue

  19. Breadth-First Search A B I E C D M K F H N O G Q R T goal P S Queue:  A

  20. Breadth-First Search A B I E C D M K F H N O G Q R T goal P S Queue:  B I E

  21. Breadth-First Search A B I E C D M K F H N O G Q R T goal P S Queue:  C D I E

  22. Breadth-First Search A B I E C D M K F H N O G Q R T goal P S Queue:  N D I E

  23. Breadth-First Search A B I E C D M K F H N O G Q R T goal P S Queue:  P S D I E

  24. Breadth-First Search A B I E C D M K F H N O G Q R T goal P S Queue:  S D I E

  25. Breadth-First Search A B I E C D M K F H N O G Q R T goal P S Queue:  D I E

  26. Breadth-First Search A B I E C D M K F H N O G Q R T goal P S Queue:  I E

  27. Breadth-First Search A B I E C D M K F H N O G Q R T goal P S Queue:  M K E

  28. Breadth-First Search A B I E C D M K F H N O G Q R T goal P S Queue:  O G K E

  29. Breadth-First Search A B I E C D M K F H N O G Q R T goal P S Queue:  G K E

  30. Breadth-First Search A B I E C D M K F H N O G Q R T goal P S DONE!!! Solution: A  I  M  G Queue:  K E

  31. Example: The 8-Puzzle • States? integer location of tiles • Operators? move blank left, right, up, down • Goal Test? = goal state (given) • Path Cost? One per move

  32. Example: 8-Puzzle – Depth First Search We will assume that we can do repeated state checking (i.e., we will not generate nodes that have been previously expanded)

  33. Example: 8-Puzzle – Depth First Search

  34. Example: 8-Puzzle – Depth First Search

  35. Example: 8-Puzzle – Depth First Search

  36. Example: 8-Puzzle – Depth First Search

  37. Example: 8-Puzzle – Depth First Search

  38. Example: 8-Puzzle – Depth First Search

  39. . . . Example: 8-Puzzle – Depth First Search

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