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Searching Algorithms

Searching Algorithms. Breadth First Search and Depth First Search. Why Search?. Greatest problem in Computer Science Has lead to a lot of new ideas and data structures Search engines before G oogle dawned were very slow. Search engines even took 10 minutes to search.

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Searching Algorithms

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  1. Searching Algorithms Breadth First Search and Depth First Search

  2. Why Search? • Greatest problem in Computer Science • Has lead to a lot of new ideas and data structures • Search engines before Google dawned were very slow. Search engines even took 10 minutes to search.

  3. Trees were created to store data • Finding the data requires searching • Graph searching and Tree Searching algorithms that we are going to learn today are BFS and DFS.

  4. Breadth First Search • b- branching • d - depth 1 4 2 3 10 9 5 6 5 6 7 7 8

  5. Breadth First Search 1 4 2 3 10 9 5 6 5 6 7 7 8

  6. Breadth First Search 1 4 2 3 10 9 5 6 5 6 7 7 8

  7. Breadth First Search 1 4 2 3 10 9 5 6 5 6 7 7 8

  8. Breadth First Search 1 4 2 3 10 9 5 6 5 6 7 7 8

  9. Breadth First Search 1 4 2 3 10 9 5 6 5 6 7 7 8

  10. Properties of BFS • Worst case performance – O(bd) • Worst case space complexity - O(bd) • Implemented using a queue. But you are free to experiment with other data structures

  11. Assignment:

  12. Depth First Search

  13. Depth First Search • b – branching • d - depth 1 4 2 3 10 9 5 6 5 6 7 7 8

  14. Depth First Search 1 4 2 3 10 9 5 6 5 6 7 7 8

  15. Depth First Search 1 4 2 3 10 9 5 6 5 6 7 7 8

  16. Depth First Search 1 4 2 3 10 9 5 6 5 6 7 7 8

  17. Depth First Search 1 4 2 3 10 9 5 6 5 6 7 7 8

  18. Depth First Search 1 4 2 3 10 9 5 6 5 6 7 7 8

  19. Depth First Search 1 4 2 3 10 9 5 6 5 6 7 7 8

  20. Depth First Search 1 4 2 3 10 9 5 6 5 6 7 7 8

  21. Can you guess the Time and Space complexity of the DFS?

  22. Can you guess the Time and Space complexity of the DFS? • Yes, Time complexity of DFS is O(bd)

  23. Properties of DFS • Worst case performance – O(bd) • Worst case space complexity - O(d) • Implemented using a queue. But you are free to experiment with other data structures

  24. Answer for Breadth First Assignment

  25. Are you sure you know BFS and DFS? • What will you do if there is a loop in DFS? What are the data structures to use? • In order to reduce space complexity in BFS, why don’t we just delete all the nodes that are visited until the previous depth?

  26. THANK YOU!!- Mino De Raj

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