Introduction and a Review of Basic Concepts

1
Introduction and a Review of Basic Concepts

• Syllabus and goals of the course
• Object oriented programming contrasting to C
  programming
• Objects, classes, methods
• Instantiation, references
• Polymorphism, inheritance
• Constructor, destructor, garbage collection
• Encapsulation
• Public, private, protected
• Data structures already introduced Stacks,
  queues, linked lists
• Recursion and induction

Understanding data structures and algorithms is a
major difference separating computer scientists
from one who reads a manual and begins to program.
2
C versus Java

• The dot in Java is equivalent to the -gt C there
  is no Java equivalent to the C dot operator.
  Generally, use -gt in most cases and declare
  variables using the (indicating pointer)
• There is no Boolean in C. Many programmers
  declare TRUE and FALSE using define
• C has no garbage collection. To avoid memory
  leaks, make sure to free whatever you malloc.
• Use NULL in C, instead of the null in Java
• Use scanf for input, but make sure to clear the
  input buffer after an error (scanf("s"))
• C has no methods (it has functions), so dot
  notation makes no sense. Replace object.method
  by function(data
• There is no length property in arrays and
  strings. Array sizes must be stored in a separate
  variable.
• Be careful with pointers and memory management. C
  doesnt catch all errors at compile time.

3
Strings in C

• There is no String type, use an array of
  characters (char data).
• C has no operator for string concatenation.
  Use strcat, but make sure you have an allocated
  area in memory to hold the larger string.
• To truncate a string, store '\0' in the
  appropriate index.
• To format output, use printf.
• For both puts and printf, make sure to follow the
  output with fflush(stdout). Otherwise, output
  only occurs when the accumulated print buffer
  gets large enough.
• There are many string functions in C, all
  starting with str. There is also memory
  manipulation functions, all starting with mem.
• Make sure your strings end with a null. Java has
  the length in the front of a string C has a null
  at the end.

4
Analysis of Algorithms

• Definition of Algorithm. Why study data types
  and algorithm?
• Step-by-step solution to a problem
• Often the problem can be specified in terms of
  the size of the data set (n).
• Algorithm performance (The technical term is
  complexity)
• A good algorithm implemented by a bad programmer
  will beat a bad algorithm implemented by a good
  programmer
• A time function, f, of the dataset size is often
  used to measure effectiveness as the data set
  size grows. For example, f(n) lt cn, where c is
  a constant gt 0. Other examples of the growth
  rate are cn2, clg n, c, lg2 n, etc.
• Big Oh notation.
• How to determine if an algorithm is a good one?
• How fast does it work on a given data set?
• What is the Relationship between time and data
  set size?
• How does it perform on different data set sizes?
• Growth is more important than a given runs
  performance

5
Big Oh Notation
Measurement of algorithm efficiency in terms of
memory or time as the problem size increases

• Formal Definition f(n) O(g(n)) means there are
  positive constants c and z, such that 0 f(n)
  cg(n) for all n z. The values of c and z must
  be fixed for the function f and must not depend
  on n.
• Explanation of terms
• g(n) is a well known function to which we want to
  compare our algorithm.
• f(n) is how our algorithm performs on different
  size data sets
• z is an integer. For all data set sizes smaller
  than z, we dont consider the algorithms
  efficiency
• c is a positive constant . By multiplying g by
  this constant, all functions with equal or
  smaller slopes will satisfy the Big Oh definition
  requirements.

Review of logarithms. Conversion of logarithms
Logn x logq x / logq n
6
Pictorial View of Big Oh
Time or memory
z
Data set size
7
Allocate Unique Random Numbers

• Declare the free listint freeListMAX
• Initialize the free listfor (i0 iltMAX i)
  freeListi ifreeCount MAX
• Allocate an entry from the free list
• Find a random index into the free list index
  (int)(rand() freeCount)
• Get the value from the free list (key
  freeListindex)
• Replace the index with the last value in the
  freeListfreeListindex freeList--freeCount
  
• Release an entry back to the free list
• Put the value to the end of the free
  listfreeListfreeCount key

8
Abstract Data TypeA general-purpose data
structure encapsulated from the user through a
well-defined set of operation

• Design
• Design the operations that are to be used
• Design the data structure to be used
• Examples (What operations? What data-structure?)
• Javas primitive floating point number
• Stacks, queues, and linked lists.
• To be covered Trees, priority queues, hash
  tables, graphs.
• Arrays (Ordered and Unordered)
• Array operations and complexities (insert,
  delete, find, expand,sort,access,traverse)
• Advantages and disadvantages