1. quickSort Algorithm 1. If first < last then begin 2. Partition the elements in the subarray first..last so that the pivot value is in place (in position pivIndex) 3. Apply quickSort to the first subarray first..pivIndex-1 4. Apply quickSort to the second subarray pivIndex+1..last end The two stopping cases are: 1. (first = last) -- only one value in subarray so sorted! 2. (first > last) -- no values in subarray so sorted!

2. How do we Partition? 1. Define the pivot value as the contents of val[first] 2. Initialize up to first and uown to last 3. Repeat 4. Increment up until up selects the first element greater than the pivot value 5. Decrement down until it selects the first element less than or equal to the pivot value 6. if up < down exchange their values until up meets or passes down 7. Exchange val[first] and val[down] 8. Define pivIndex as down

3. quickSort Example 447523435512647733 012345678 firstlast

4. Has first exceeded last? 447523435512647733 firstlast 012345678

5. Has first exceeded last? 447523435512647733 firstlast NO! 012345678

6. Define the value in position first to be the pivot 447523435512647733 firstlast 012345678

7. Define the value in position first to be the pivot 447523435512647733 firstlast pivot 44 012345678

8. Define up to be first and down to be last 447523435512647733 firstlast pivot 44 012345678

9. Define up to be first and down to be last 447523435512647733 updown pivot 44 firstlast 012345678

10. Move up to the first value > pivot 447523435512647733 updown pivot 44 firstlast 012345678

11. Move up to the first value > pivot 447523435512647733 updown pivot 44 firstlast 012345678

12. Move down to the first value <= pivot 447523435512647733 updown pivot 44 firstlast 012345678

13. Move down to the first value <= pivot 447523435512647733 updown pivot 44 firstlast 012345678

14. Exchange these values 447523435512647733 updown pivot 44 firstlast 012345678

15. Exchange these values 443323435512647775 updown pivot 44 firstlast 012345678

16. Move up to the first value > pivot 443323435512647775 updown pivot 44 firstlast 012345678

17. Move up to the first value > pivot 443323435512647775 updown pivot 44 firstlast 012345678

18. Move down to the first value <= pivot 443323435512647775 updown pivot 44 firstlast 012345678

19. Move down to the first value <= pivot 443323435512647775 updown pivot 44 firstlast 012345678

20. Exchange them 443323431255647775 updown pivot 44 firstlast 012345678

21. Move up to the first value > pivot 443323431255647775 updown pivot 44 firstlast 012345678

22. Move up to the first value > pivot 443323431255647775 updown pivot 44 firstlast 012345678

23. Move down to the first value <= pivot 443323431255647775 updown pivot 44 firstlast 012345678

24. Move down to the first value <= pivot 443323431255647775 updown pivot 44 firstlast 012345678

25. up and down have passed each other, so exchange the pivot value and the value in down 443323431255647775 updown pivot 44 firstlast 012345678

26. up and down have passed each other, so exchange the pivot value and the value in down 443323431255647775 updown pivot 44 firstlast 012345678

27. up and down have passed each other, so exchange the pivot value and the value in down 123323434455647775 pivIndex down pivot 44 firstlast 012345678

28. Note that all values below pivIndex are <= pivot 123323434455647775 pivIndex pivot 44 firstlast 012345678

29. and all values above pivIndex are > pivot 123323434455647775 pivIndex pivot 44 firstlast 012345678

30. This gives us two new subarrays to Partition 123323434455647775 pivIndex pivot 44 first 1 last 2 first 2 last 1 012345678

31. quickSort Procedure Code public void quickSort ( int [ ] a, int first, int last ) { int pivIndex; if ( first < last ) { pivIndex = partition ( a, first, last ); quickSort ( a, first, pivIndex-1 ); quickSort ( a, pivIndex+1, last ); }