Binary search

# Binary search

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## Binary search

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##### Presentation Transcript

1. 1. Mr Greedy 2. Mr Grumpy 3. Mr Happy 4. Mr Nosey 5. Mr Rush 6. Mr Small 7. Mr Strong 8. Mr Tall 9. Mr Tickle 10. Mr Topsy-Turvy ? Mr Nosey? Binary search This algorithm is for finding an item in a sorted list or determining that it is not in the list. Is Mr Nosey in the list opposite? First find the middle of the list: (10+1)/2 = 5.5 so take 6th item Compare Mr Nosey and Mr Small, Nosey comes before Small so reduce the list to the first half.

2. 1. Mr Greedy 2. Mr Grumpy 3. Mr Happy 4. Mr Nosey 5. Mr Rush 6. Mr Small 7. Mr Strong 8. Mr Tall 9. Mr Tickle 10. Mr Topsy-Turvy 1. Mr Greedy 2. Mr Grumpy 3. Mr Happy 4. Mr Nosey 5. Mr Rush ? Mr Nosey? Binary search Now find the middle (1+5)/2 = 3rd item Compare Mr Nosey and Mr Happy , Nosey comes after Happy so reduce the list to the second half.

3. 1. Mr Greedy 2. Mr Grumpy 3. Mr Happy 4. Mr Nosey 5. Mr Rush 6. Mr Small 7. Mr Strong 8. Mr Tall 9. Mr Tickle 10. Mr Topsy-Turvy 4. Mr Nosey 5. Mr Rush 1. Mr Greedy 2. Mr Grumpy 3. Mr Happy 4. Mr Nosey 5. Mr Rush ? Mr Nosey? Binary search Find the middle (4+5)/2 = 4.5 so take item 5 Compare Mr Nosey and Mr Rush, Nosey comes before Rush so take first half of list

4. 1. Mr Greedy 2. Mr Grumpy 3. Mr Happy 4. Mr Nosey 5. Mr Rush 6. Mr Small 7. Mr Strong 8. Mr Tall 9. Mr Tickle 10. Mr Topsy-Turvy 4. Mr Nosey 5. Mr Rush 4. Mr Nosey 1. Mr Greedy 2. Mr Grumpy 3. Mr Happy 4. Mr Nosey 5. Mr Rush ? Mr Nosey? Binary search Compare Mr Nosey and Mr Nosey, We have found him!