CS 24 – Problem Solving II (Data Structures)

1. CS 24 – Problem Solving II (Data Structures) Diana Franklin

2. Course Objectives • Become a programmer • More mature through practice • Pointers, linked structures • Recursion • Data structures

3. Course Objectives • Manage Complexity – Complex systems change the world • Analysis to make decisions on algorithms • Choose proper data structures • Learn object-oriented programming

4. Code Complexity • Google, Google, Google – how has it changed the world? • Hundreds of programs execute for one query • Millions of queries each day • Web crawlers gathering data • E-mails being read and sent • Photos in Google+ and Picasa • Everything is connected

5. Big Data, Genomics, and Cancer • 2010: Complete genomic characterization of a rare cancer tumor of one patient helped in clinical decision making and in identifying therapeutic approaches where no established treatment protocols existed • 1st use of genomics to inform choice of cancer treatment options, stabilize cancer • 34 researchers kept patient alive 6 months [1] Jones et al. (British Columbia Cancer Center): Evolution of an adenocarcinoma in response to selection by targeted kinase inhibitors. Genome Biology 2010 11:R82.

6. Big Data, Genomics, and Cancer • Circos graph to compare genomes • CNV: chromosomal copy number variation • LOH: loss of heterozygosity • T1 pre-treatment tumor cell • T2 post-treatment tumor cell • Δ degree of change between 2 cancers • R normal cell Large regions of Chromosomal loss

7. Big Data, Genomics, and Cancer • Led to hypothesis of mechanism driving tumor and drugs to target it • Clinic applied drug not approved for disease • Shrank tumors by 22%, no new lesions • Not cure, but stabilized rare cancer Could we economically scale up from 34 researchers/1 patient in 3 months to a million patients per year?

8. Ways to optimize programs

9. Ways to optimize programs • faster • easy for programmer to understand • easy for user to understand • as little memory usage as possible • modular code – clear code & faster programming, reusability • scalability (throughput) • well organized • correctness • compatibility

10. Getting a taste • Algorithms to find item in the phone book • Ways to store information • Choices: List, Tree, Graph • Google+ Circles • LA Freeway system • Management Structure of an Organization

11. Searching for a number in a phone book that has n numbers in it • Start at the beginning • Best case - • Average case – • Worst case -

12. Searching for a number in a phone book that has n numbers in it • Start at the beginning • while (we haven’t found it) • advance to the next one • Best case - 1 • Average case – n/2 • Worst case - n

13. Searching for a number in a sorted phone book • Look at the middle element • best-case - • worst-case • average-case –

14. Searching for a number in a sorted phone book • Look at the middle element • if it’s smaller than that one, throw out top half • if it’s larger than that one, throw out bottom half • repeat until we have only one item left • best-case - • worst-case • average-case –

15. Searching for a number in a sorted phone book • Look at the middle element • if it’s smaller than that one, throw out top half • if it’s larger than that one, throw out bottom half • repeat until we have only one item left • best-case - 1 • worst-case log2(n) • average-case –summation of: time*probability of that time • 1*1/n + 2*2/n + 3*4/n + 4*8/n+…+log2(n)*n/2

16. n*1/2*1/2*1/2*… = 1 • n*(1/2)^j = 1 • 1/(2^j) = 1/n • n = 2^j • log2(n) = j

17. Curricular Approach

18. Spiral Approach • Present the same topic multiple times • More depth the second time • Presented by a different person • Reinforce earlier learning while encouraging new perspective

19. Spiral Approach • Reinforced topics • Arrays, File I/O, Command-Line Args • Pointers, Recursion • New topics, deep coverage • Linked structures (lists, queues, trees) • Classes • New topics, shallow coverage • advanced object-oriented concepts, complexity

20. Why so many languages? • Python – candy – bribe students with flashy, simple applications. Hide details • C – veggies – Expose details. Mastery necessary for OS, networks, compilers, etc. • C++ - fruit – Introduce objects as programs get more complex.

21. Assignment Philosophy • Success is based on what you DO, not what you ARE • College requires better work habits than in high school, upper-division more than lower • Instill / Encourage / Reward good habits in lower division • Give more freedom in upper division

22. http://www.cs.ucsb.edu/~franklin/24/ • Syllabus • Assignments (with dates) • Lecture resources • Definition of plagiarism – never work in groups of 3+ • Detailed grading breakdown • Late policy – 24 hours, 10% off • Information guides for gdb, compiling, unix • etc, etc, etc.

23. Logistics • Labs – attendance mandatory • Mini-Exams – 2 – in between to make sure I don’t lose you • Exams – 2 midterms, 1 final • Programs – Some individual, some pair programming • Participation Extra Credit – asking / answering questions in class

24. Lab tomorrow • If you have a CoE account, sit at a computer right away • If you do not have a CoE account, join someone who is already at a computer • You may switch partners in later labs once everyone has accounts

25. Waiting List • Everyone on the waiting list who had the pre-reqs is making it in the class • The class is completely, completely full (slightly overenrolled) with those students • benji@cs.ucsb.edu, franklin@cs.ucsb.edu

26. Any Logistical Questions?

27. Arrays • How is an array different from a pointer? • int *x • int x[10]; • What does this declare? • int *x[10]; • int **x;

28. Arrays vs Pointers • How do you access arrays vs pointers? • int x[10]; • int *y = (int *)malloc(sizeof(int)*10); • They are mostly the same: • x[5] = 10; y[5] = 10; • *(x+5) = 10; *(y+5) = 10; • The big differences: • y = whatever; // can’t do x = anything • free(y); // don’t free x

29. Strings • How are strings stored in C? • How do you declare an array of strings?

30. Strings • How are strings stored in C? • array of characters • end with a hidden ‘\0’ • How do you declare an array of strings?

31. Strings • How are strings stored in C? • array of characters • end with a hidden ‘\0’ • How do you declare an array of strings? • char **strings; • char *strings[10];

32. Pointer Review

33. Pointer Review • General knowledge • Drawing the memory • Reading and Writing

34. What do you know about pointersthat was covered in CS 16?

35. What do you know about pointersthat was covered in CS 16? • They store an address in a variable • You can have a pointer pointing to another pointer • You can change values in arrays more easily • There are void pointers, and you need to cast them if you want to dereference them • Pointers are used for dynamic memory allocation

36. Draw the memory of each int *x, *y; x = &a; y = &b; x = y; int a, b; a = 5; b = 3; a = b; What is the difference between (a = b) and (x = y) for what the computer does? What is the difference between (a = b) and (x = y) for how we view them? The way to make working with pointers easy is to operate on them mechanically like the computer. They are no different than integers.

37. Pointer Review – what prints out? int x = 3, y = 4; int *pX = &x, *pY = &y; (pX == pY) ? Print(“Same\n”): print(“Not Same\n”); (*pX == *pY) ? Print(“Equal\n”) : print(“NEqual\n”); x = y (pX == pY) ? Print(“Same\n”): print(“Not Same\n”); (*pX == *pY) ? Print(“Equal\n”) : print(“NEqual\n”); x = 10; pX = pY; (pX == pY) ? Print(“Same\n”): print(“Not Same\n”); (*pX == *pY) ? Print(“Equal\n”) : print(“NEqual\n”);

38. Structs • What do you know about structs? • member variables or fields • you can have structs inside of structs inside of structs… • organizes your data • composite data type • you can put them in an array (just like any other type) • create many variables of that type

39. Structs • What do you know about structs? • You can create your own data type • Make many copies of that data type • dynamically allocate structs • Variables with multiple fields – programmer defines what the fields hold

40. Structs typedefstructblah { struct blah { int weight; int weight; floatprice; float price; } fazizzle; }; typedefintfjlsajfjaeisje How do I declare three variables, named apple, banana, and melon, of type struct blah or fazizzle? structblah apple, banana, melon; fazizzleorange, pineapple, kiwi; apple.weight = 5;

41. Structs typedefstruct _product { int weight; floatprice; } product; How do I declare three variables, named apple, banana, and melon, of type product? struct _product apple, banana, melon; product apple, banana, melon; apple.weight = 5;

42. Structs typedefstruct _product { int weight; floatprice; } product; product apple; product banana, melon;

43. Structs typedefstruct _product { int weight; floatprice; } product; product apple, banana, melon; How do I set the weight field of apple?

44. Structs typedefstruct _product { int weight; floatprice; } product; product apple, banana, melon; product *pApple, *pBanana, *pMelon; pApple = &apple; pBanana = &banana; pMelon = & melon; How do I set the weight field of apple? apple.weight = 5; pApple->weight = 5; (*pApple).weight = 5;

45. Structs typedefstruct _product { int*weight; floatprice; } product; product apple, banana, melon; product *pApple, *pBanana, *pMelon; pApple = &apple; pBanana = &banana; pMelon = & melon; How do I set the weight field of apple? *(apple.weight) = 5; apple.weight[10] = 5 *(pApple->weight) = 5; (*pApple).weight = 5;

46. When should we use pointers instead of non-pointers? • If you have a local variable you want to use, but the memory has already been allocated • Dynamic size: If you want to be to vary size OR you don’t know how big it is going to be • Time: You don’t want to copy the whole piece of data. Just pass a pointer to it. • Accessibility: You want the function being called to be able to change values in the caller’s memory • Lifetime: You want to create something that lives past the end of the function call’s life. You create it and pass its address out of the function. • Pointers can change around: you have a “label” or variable that pointers to different things through time, but those things never get destroyed.

47. Linking pointers Typdefstruct_node{ int value; struct_node*next; } node; node l1, l2, l3, l4; node*p1, *p2, *p3, *p4; p1 = &l1; p2 = &l2; p3 = &l3; p4 = &l4; l1.value = 1; l2.value = 2; l3.value = 4; l4.value = 8; p1->next = p2; p2->next = p3; p3->next = p4; p4->next = p1; p1->value = 5; p1->next->value = 3; p1->next->next->value = 7; for(i=0;i<4;i++) { printf(“%d, “,p2->value); p2 = p2->next; } p2 = null; p3 = null; p4 = null;

48. Let’s remove l3 from the list w/out using l1, l2, l3, l4