Computer Science 101 A Survey of Computer Science

1. Computer Science 101A Survey of Computer Science Sorting

2. Sorting • Some of the most heavily used algorithms are those for sorting data. • Arranging data into numerical or alphabetical order for purposes of • Reports by category • Summarizing data • Searching data

3. Sorting (cont) • Given: n, N1,N2,…,Nn • Want: Rearrangement M1,M2,…,Mn where M1…  Mn according to the appropriate understanding of . • There are many well-known algorithms for doing this. Preference may be due to • List size • Degree of order already present • Ease of programming • Program available

4. Sorting - Selection Sort • Strategy: • Find the largest element in list. • Swap it with last element in list. • Find next largest. • Swap it with next to last element in list • Etc. • Variables: • U - Marker for unsorted section • L - Position of largest so far • C - Current position

5. Selection Sort - The algorithm Set U to nWhile U>1 Set L to 1 Set C to 2 While C ≤ U do If N(C) > N(L) then Set L to C Set C to C+1 end-of-loop Exchange N(L) and N(U) Set U to U-1end-of-loopStop

6. L U L U 5 19 12 5 19 12 6 6 9 9 6 9 9 6 9 9 9 6 6 9 6 L U C C 5 19 C U L 5 19 12 L U C U 19 5 12 L 5 12 19 C C L U 12 5 19 12 C Selection Sort - Example (Pass 1) 12

7. L U L U 5 12 12 5 19 6 9 9 6 9 6 6 9 6 9 6 19 C C L U L U 5 12 19 5 19 12 C C L U 9 5 12 19 C L U 12 19 5 C Selection Sort - Example (Pass 2)

8. L U 12 6 6 6 6 6 C L U 5 12 19 5 9 19 C 9 LU 19 5 9 12 19 C L L U U 5 5 9 9 12 12 19 19 C C Selection Sort - Example (Pass 3)

9. L U U 5 9 12 19 6 9 12 19 5 6 5 6 C L U 5 12 C LU 9 12 19 6 C 9 19 Selection Sort - Example (Pass 4)

10. Sorting - Bubble Sort • Strategy: • Pass through the list from left to right. • Compare each element with the one to its left. • Swap them if they are out of order. • Such a pass will put largest at the right end. • Continue making these passes until sorted. • Variables: • U - Marker for unsorted section • C - Current position

11. Bubble Sort - The algorithm Set U to nWhile U > 1 do Set C to 2 While C ≤ U do If N(C) < N(C-1) then Exchange N(C) and N(C-1) Set C to C+1 end-of-loop Set U to U-1end-of-loopStop

12. U U 5 19 3 9 6 3 6 5 5 5 9 5 6 6 19 3 C C U U 9 19 3 9 19 C C 6 U 19 3 9 C Bubble Sort - Example (Pass 1)

13. U 9 6 3 9 5 3 5 5 3 5 19 C U C 9 6 19 C 6 6 3 9 U U 19 19 C Bubble Sort - Example (Pass 2)

14. U U U 9 9 5 5 5 9 C C 6 6 3 6 3 3 19 19 19 C Bubble Sort - Example (Pass 3)

15. 3 9 9 9 3 5 U U U C 3 5 5 6 6 6 C 19 19 19 Bubble Sort - Example (Pass 4)

16. You take the big uns and I'll get the little doggies!