1. Computer Science 101 A Survey of Computer Science
Searching

2. Searching Searching is one of the most common operations of computing
Search for student record based on id
Search for “best” item based on some criteria
Search for airline reservations
Clearly we know all there is to know about searching

3. Or do we?

4. Or do we?

5. Or do we?

6. Or do we?

7. Or do we?

8. Sequential Search Algorithm
Given: List of values v1,v2,…,vn Target value, T
Output: Information about T if in list and message if T is not in list
Strategy:
Use variables:
i for current location in list
Found to indicate whether T located or not
Initialize i=1, Found=false
Pass through the list sequentially

9. Sequential Search-Names/Phone No’s
Given: Names N1,N2,…Nn Target NAME Phone No’s T1,T2,…,Tn
Output: Phone number of NAME
Note: We’ll use this as an example for sequential search, but if the names are in alphabetical order there is a much better algorithm.

10. Names/Phone No’s Algorithm
Set Found to false
Set i to 1
While not Found and i ≤ last position Do
if Ni = NAME then
Print Ti
Set Found to true
else
Set i to i+1 end-of-loop
if Found=false then
Print ‘Sorry, not in directory’
Stop

11. Algorithm to Find Largest
Given: List of numbers A1,A2,…,An
Output: Largest value in list and its position
Strategy:
Use variables:
i for current location in list
Largest for largest value found so far
LargeLoc for position of largest found so far
Initialize Largest=A1,LargeLoc=1,i=2
Pass through the list sequentially

12. Algorithm to Find Largest (cont)
Set Largest to A1
Set LargeLoc to 1
Set i to 2
While i  n do
if Ai > Largest then
Set Largest to Ai
Set LargeLoc to i
Set i to i+1
end-of-loop
Print Largest, LargeLoc
Stop

13. Example: 1. Set Largest to A1 2. Set LargeLoc to 1 3. Set i to 2
1. Set Largest to A1
2. Set LargeLoc to 1
3. Set i to 2
4. While i  n do
5. if Ai > Largest then
Set Largest to Ai
Set LargeLoc to i
8. Set i to i+1
9. end-of-loop
10. Print Largest, LargeLoc
11. Stop
Largest LargeLoc i n 8

14. Example: 1. Set Largest to A1 2. Set LargeLoc to 1 3. Set i to 2
1. Set Largest to A1
2. Set LargeLoc to 1
3. Set i to 2
4. While i  n do
5. if Ai > Largest then
Set Largest to Ai
Set LargeLoc to i
8. Set i to i+1
9. end-of-loop
10. Print Largest, LargeLoc
11. Stop
Largest LargeLoc i n

15. Example: 1. Set Largest to A1 2. Set LargeLoc to 1 3. Set i to 2
1. Set Largest to A1
2. Set LargeLoc to 1
3. Set i to 2
4. While i  n do
5. if Ai > Largest then
Set Largest to Ai
Set LargeLoc to i
8. Set i to i+1
9. end-of-loop
10. Print Largest, LargeLoc
11. Stop
Largest LargeLoc i n

16. Example: 1. Set Largest to A1 2. Set LargeLoc to 1 3. Set i to 2
1. Set Largest to A1
2. Set LargeLoc to 1
3. Set i to 2
4. While i  n do
5. if Ai > Largest then
Set Largest to Ai
Set LargeLoc to i
8. Set i to i+1
9. end-of-loop
10. Print Largest, LargeLoc
11. Stop
Largest LargeLoc i n

17. Example: 1. Set Largest to A1 2. Set LargeLoc to 1 3. Set i to 2
1. Set Largest to A1
2. Set LargeLoc to 1
3. Set i to 2
4. While i  n do
5. if Ai > Largest then
Set Largest to Ai
Set LargeLoc to i
8. Set i to i+1
9. end-of-loop
10. Print Largest, LargeLoc
11. Stop
Largest LargeLoc i n

18. Example: 1. Set Largest to A1 2. Set LargeLoc to 1 3. Set i to 2
1. Set Largest to A1
2. Set LargeLoc to 1
3. Set i to 2
4. While i  n do
5. if Ai > Largest then
Set Largest to Ai
Set LargeLoc to i
8. Set i to i+1
9. end-of-loop
10. Print Largest, LargeLoc
11. Stop
Largest LargeLoc i n

19. Example: 1. Set Largest to A1 2. Set LargeLoc to 1 3. Set i to 2
1. Set Largest to A1
2. Set LargeLoc to 1
3. Set i to 2
4. While i  n do
5. if Ai > Largest then
Set Largest to Ai
Set LargeLoc to i
8. Set i to i+1
9. end-of-loop
10. Print Largest, LargeLoc
11. Stop
Largest LargeLoc i n

20. Example: 1. Set Largest to A1 2. Set LargeLoc to 1 3. Set i to 2
1. Set Largest to A1
2. Set LargeLoc to 1
3. Set i to 2
4. While i  n do
5. if Ai > Largest then
Set Largest to Ai
Set LargeLoc to i
8. Set i to i+1
9. end-of-loop
10. Print Largest, LargeLoc
11. Stop
Largest LargeLoc i n

21. Example: 1. Set Largest to A1 2. Set LargeLoc to 1 3. Set i to 2
1. Set Largest to A1
2. Set LargeLoc to 1
3. Set i to 2
4. While i  n do
5. if Ai > Largest then
Set Largest to Ai
Set LargeLoc to i
8. Set i to i+1
9. end-of-loop
10. Print Largest, LargeLoc
11. Stop
Largest LargeLoc i n

22. Example: 1. Set Largest to A1 2. Set LargeLoc to 1 3. Set i to 2
1. Set Largest to A1
2. Set LargeLoc to 1
3. Set i to 2
4. While i  n do
5. if Ai > Largest then
Set Largest to Ai
Set LargeLoc to i
8. Set i to i+1
9. end-of-loop
10. Print Largest, LargeLoc
11. Stop
Largest LargeLoc i n

23. Example: 1. Set Largest to A1 2. Set LargeLoc to 1 3. Set i to 2
1. Set Largest to A1
2. Set LargeLoc to 1
3. Set i to 2
4. While i  n do
5. if Ai > Largest then
Set Largest to Ai
Set LargeLoc to i
8. Set i to i+1
9. end-of-loop
10. Print Largest, LargeLoc
11. Stop
Largest LargeLoc i n

24. Example: 1. Set Largest to A1 2. Set LargeLoc to 1 3. Set i to 2
1. Set Largest to A1
2. Set LargeLoc to 1
3. Set i to 2
4. While i  n do
5. if Ai > Largest then
Set Largest to Ai
Set LargeLoc to i
8. Set i to i+1
9. end-of-loop
10. Print Largest, LargeLoc
11. Stop
Largest LargeLoc i n

25. Example: 1. Set Largest to A1 2. Set LargeLoc to 1 3. Set i to 2
1. Set Largest to A1
2. Set LargeLoc to 1
3. Set i to 2
4. While i  n do
5. if Ai > Largest then
Set Largest to Ai
Set LargeLoc to i
8. Set i to i+1
9. end-of-loop
10. Print Largest, LargeLoc
11. Stop
Largest LargeLoc i n

26. Example: 1. Set Largest to A1 2. Set LargeLoc to 1 3. Set i to 2
1. Set Largest to A1
2. Set LargeLoc to 1
3. Set i to 2
4. While i  n do
5. if Ai > Largest then
Set Largest to Ai
Set LargeLoc to i
8. Set i to i+1
9. end-of-loop
10. Print Largest, LargeLoc
11. Stop
Largest LargeLoc i n

27. Example: 1. Set Largest to A1 2. Set LargeLoc to 1 3. Set i to 2
1. Set Largest to A1
2. Set LargeLoc to 1
3. Set i to 2
4. While i  n do
5. if Ai > Largest then
Set Largest to Ai
Set LargeLoc to i
8. Set i to i+1
9. end-of-loop
10. Print Largest, LargeLoc
11. Stop
Largest LargeLoc i n

28. Example: 1. Set Largest to A1 2. Set LargeLoc to 1 3. Set i to 2
1. Set Largest to A1
2. Set LargeLoc to 1
3. Set i to 2
4. While i  n do
5. if Ai > Largest then
Set Largest to Ai
Set LargeLoc to i
8. Set i to i+1
9. end-of-loop
10. Print Largest, LargeLoc
11. Stop
Largest LargeLoc i n

29. Example: 1. Set Largest to A1 2. Set LargeLoc to 1 3. Set i to 2
1. Set Largest to A1
2. Set LargeLoc to 1
3. Set i to 2
4. While i  n do
5. if Ai > Largest then
Set Largest to Ai
Set LargeLoc to i
8. Set i to i+1
9. end-of-loop
10. Print Largest, LargeLoc
11. Stop
Largest LargeLoc i n

30. Example: 1. Set Largest to A1 2. Set LargeLoc to 1 3. Set i to 2
1. Set Largest to A1
2. Set LargeLoc to 1
3. Set i to 2
4. While i  n do
5. if Ai > Largest then
Set Largest to Ai
Set LargeLoc to i
8. Set i to i+1
9. end-of-loop
10. Print Largest, LargeLoc
11. Stop
Largest LargeLoc i n

31. Example: 1. Set Largest to A1 2. Set LargeLoc to 1 3. Set i to 2
1. Set Largest to A1
2. Set LargeLoc to 1
3. Set i to 2
4. While i  n do
5. if Ai > Largest then
Set Largest to Ai
Set LargeLoc to i
8. Set i to i+1
9. end-of-loop
10. Print Largest, LargeLoc
11. Stop
Largest LargeLoc i n

32. Example: 1. Set Largest to A1 2. Set LargeLoc to 1 3. Set i to 2
1. Set Largest to A1
2. Set LargeLoc to 1
3. Set i to 2
4. While i  n do
5. if Ai > Largest then
Set Largest to Ai
Set LargeLoc to i
8. Set i to i+1
9. end-of-loop
10. Print Largest, LargeLoc
11. Stop
Largest LargeLoc i n

33. Example: 1. Set Largest to A1 2. Set LargeLoc to 1 3. Set i to 2
1. Set Largest to A1
2. Set LargeLoc to 1
3. Set i to 2
4. While i  n do
5. if Ai > Largest then
Set Largest to Ai
Set LargeLoc to i
8. Set i to i+1
9. end-of-loop
10. Print Largest, LargeLoc
11. Stop
Largest LargeLoc i n

34. Example: 1. Set Largest to A1 2. Set LargeLoc to 1 3. Set i to 2
1. Set Largest to A1
2. Set LargeLoc to 1
3. Set i to 2
4. While i  n do
5. if Ai > Largest then
Set Largest to Ai
Set LargeLoc to i
8. Set i to i+1
9. end-of-loop
10. Print Largest, LargeLoc
11. Stop
Largest LargeLoc i n

35. Example: 1. Set Largest to A1 2. Set LargeLoc to 1 3. Set i to 2
1. Set Largest to A1
2. Set LargeLoc to 1
3. Set i to 2
4. While i  n do
5. if Ai > Largest then
Set Largest to Ai
Set LargeLoc to i
8. Set i to i+1
9. end-of-loop
10. Print Largest, LargeLoc
11. Stop
Largest LargeLoc i n

36. Example: 1. Set Largest to A1 2. Set LargeLoc to 1 3. Set i to 2
1. Set Largest to A1
2. Set LargeLoc to 1
3. Set i to 2
4. While i  n do
5. if Ai > Largest then
Set Largest to Ai
Set LargeLoc to i
8. Set i to i+1
9. end-of-loop
10. Print Largest, LargeLoc
11. Stop
Largest LargeLoc i n

37. Example: 1. Set Largest to A1 2. Set LargeLoc to 1 3. Set i to 2
1. Set Largest to A1
2. Set LargeLoc to 1
3. Set i to 2
4. While i  n do
5. if Ai > Largest then
Set Largest to Ai
Set LargeLoc to i
8. Set i to i+1
9. end-of-loop
10. Print Largest, LargeLoc
11. Stop
Largest LargeLoc i n

38. Example: 1. Set Largest to A1 2. Set LargeLoc to 1 3. Set i to 2
1. Set Largest to A1
2. Set LargeLoc to 1
3. Set i to 2
4. While i  n do
5. if Ai > Largest then
Set Largest to Ai
Set LargeLoc to i
8. Set i to i+1
9. end-of-loop
10. Print Largest, LargeLoc
11. Stop
Largest LargeLoc i n

39. Example: 1. Set Largest to A1 2. Set LargeLoc to 1 3. Set i to 2
1. Set Largest to A1
2. Set LargeLoc to 1
3. Set i to 2
4. While i  n do
5. if Ai > Largest then
Set Largest to Ai
Set LargeLoc to i
8. Set i to i+1
9. end-of-loop
10. Print Largest, LargeLoc
11. Stop
Largest LargeLoc i n

40. Example: 1. Set Largest to A1 2. Set LargeLoc to 1 3. Set i to 2
1. Set Largest to A1
2. Set LargeLoc to 1
3. Set i to 2
4. While i  n do
5. if Ai > Largest then
Set Largest to Ai
Set LargeLoc to i
8. Set i to i+1
9. end-of-loop
10. Print Largest, LargeLoc
11. Stop
Largest LargeLoc i n

41. Example: 1. Set Largest to A1 2. Set LargeLoc to 1 3. Set i to 2
1. Set Largest to A1
2. Set LargeLoc to 1
3. Set i to 2
4. While i  n do
5. if Ai > Largest then
Set Largest to Ai
Set LargeLoc to i
8. Set i to i+1
9. end-of-loop
10. Print Largest, LargeLoc
11. Stop
Largest LargeLoc i n

42. Example: 1. Set Largest to A1 2. Set LargeLoc to 1 3. Set i to 2
1. Set Largest to A1
2. Set LargeLoc to 1
3. Set i to 2
4. While i  n do
5. if Ai > Largest then
Set Largest to Ai
Set LargeLoc to i
8. Set i to i+1
9. end-of-loop
10. Print Largest, LargeLoc
11. Stop
Largest LargeLoc i n

43. Example: 1. Set Largest to A1 2. Set LargeLoc to 1 3. Set i to 2
1. Set Largest to A1
2. Set LargeLoc to 1
3. Set i to 2
4. While i  n do
5. if Ai > Largest then
Set Largest to Ai
Set LargeLoc to i
8. Set i to i+1
9. end-of-loop
10. Print Largest, LargeLoc
11. Stop
Largest LargeLoc i n

44. Example: 1. Set Largest to A1 2. Set LargeLoc to 1 3. Set i to 2
1. Set Largest to A1
2. Set LargeLoc to 1
3. Set i to 2
4. While i  n do
5. if Ai > Largest then
Set Largest to Ai
Set LargeLoc to i
8. Set i to i+1
9. end-of-loop
10. Print Largest, LargeLoc
11. Stop
Largest LargeLoc i n

45. Example: 1. Set Largest to A1 2. Set LargeLoc to 1 3. Set i to 2
1. Set Largest to A1
2. Set LargeLoc to 1
3. Set i to 2
4. While i  n do
5. if Ai > Largest then
Set Largest to Ai
Set LargeLoc to i
8. Set i to i+1
9. end-of-loop
10. Print Largest, LargeLoc
11. Stop
Largest LargeLoc i n

46. Example: 1. Set Largest to A1 2. Set LargeLoc to 1 3. Set i to 2
1. Set Largest to A1
2. Set LargeLoc to 1
3. Set i to 2
4. While i  n do
5. if Ai > Largest then
Set Largest to Ai
Set LargeLoc to i
8. Set i to i+1
9. end-of-loop
10. Print Largest, LargeLoc
11. Stop
Largest LargeLoc i n

47. Example: 1. Set Largest to A1 2. Set LargeLoc to 1 3. Set i to 2
1. Set Largest to A1
2. Set LargeLoc to 1
3. Set i to 2
4. While i  n do
5. if Ai > Largest then
Set Largest to Ai
Set LargeLoc to i
8. Set i to i+1
9. end-of-loop
10. Print Largest, LargeLoc
11. Stop
Largest LargeLoc i n

48. Example: 1. Set Largest to A1 2. Set LargeLoc to 1 3. Set i to 2
1. Set Largest to A1
2. Set LargeLoc to 1
3. Set i to 2
4. While i  n do
5. if Ai > Largest then
Set Largest to Ai
Set LargeLoc to i
8. Set i to i+1
9. end-of-loop
10. Print Largest, LargeLoc
11. Stop
Largest LargeLoc i n

49. Example: 1. Set Largest to A1 2. Set LargeLoc to 1 3. Set i to 2
1. Set Largest to A1
2. Set LargeLoc to 1
3. Set i to 2
4. While i  n do
5. if Ai > Largest then
Set Largest to Ai
Set LargeLoc to i
8. Set i to i+1
9. end-of-loop
10. Print Largest, LargeLoc
11. Stop
Largest LargeLoc i n

50. Example: 1. Set Largest to A1 2. Set LargeLoc to 1 3. Set i to 2
1. Set Largest to A1
2. Set LargeLoc to 1
3. Set i to 2
4. While i  n do
5. if Ai > Largest then
Set Largest to Ai
Set LargeLoc to i
8. Set i to i+1
9. end-of-loop
10. Print Largest, LargeLoc
11. Stop
Largest LargeLoc i n
OUTPUT: 15, 6

51. I guess we could call them Cow1, Cow2, Cow3, ...