Algorithms_and_Data_Structures_09 - Lecture 9 Computer...

Computer Science
Algorithms and Data Structures
Prof. Dr. Andreas Nüchter
Research I, Room 105
Jacobs University Bremen
http://www.nuechti.de [email protected]
Lecture 9

Algorithms and Data Structures
Dr. Andreas Nüchter
October 1, 2009
299
Announcements (1)
• Midterm
– October 15 14:15-15:30
– Remember grading policy:
• Assignments: 20% of the final grade
• Midterm: 30% of the final grade
• Final exam: 50% of the final grade
– Midterm has 3 parts:
1. Applying discussed algorithms to problems
2. Solving problems similar to homework
3. Solving new problems
– October 8 review and discussion session
– Prepare a handwritten A5 ( 148 mm × 210 mm ) crib/cheat
sheet

Algorithms and Data Structures
Dr. Andreas Nüchter
October 1, 2009
300
Announcements (2)
• Programming Assignment is out!
• Use C/C++ as programming language and make use
of the code I am providing!
• Work in Pairs!
• You have to demonstrate the software to the TAs
• Make an appointment with one of the TAs!
– Write your and you partner’s name in the list @ my office
door!

Last Lecture
• Formal proof of the theorem:
Theorem : The average number of comparisons for
sorting keys is
– We need to minimize the path length of the corresponding
decision tree
– An optimal decision tree has two
child nodes for a comparison node
• Sorting in linear time with
counting sort
• Introduction to Data Structures

Queues
• Dynamic set
• Delete operation is called de-queue
• Inset operation is called en-queue
• FIFO principle (First In First Out), i.e., the element
that is removed from the queue is the oldest one in
the queue.
• Queue can also be realized using an array
• Queue with 5 elements at the places

Queues
• after the operations ,
and
• returns the value 15.

Queues

Algorithms and Data Structures
Dr. Andreas Nüchter
October 1, 2009
305
Pointer in C/C++

Algorithms and Data Structures
Dr. Andreas Nüchter
October 1, 2009
306
Pointer in C/C++
• Address
– A place in memory, where the data is stored
– The address of variable x is obtained by &x
• Pointer
– A variable that holds an address
int i = 10;
int * j = & i; /* j "points" to i */
0x123aa8
10
0x123aa8 i
name address contents
0x123aab
j

Algorithms and Data Structures
Dr. Andreas Nüchter
October 1, 2009
307
Pointer in C/C++
• The data to which a pointer points is accessable
with the * -operator
&j is the address of i
*j is the content of the memory at place j
* -operator for dereferencing
• Meanings of * in C/C++
1. Multiplication
2. Declaration of a pointer
3. Dereferencing
int i = 10;
int *j = &i;
printf("i = %d\n", i);
printf("j = %x\n", j);
printf("j points to: %d\n", * j);

Algorithms and Data Structures
Dr. Andreas Nüchter
October 1, 2009
308
Pointer in C/C++
• Let‘s use it ☺
int i = 10;
int *j = &i;
int ** k = &j;
printf("%x\t%d\n", &i, i);
printf("%x\t%x\t%d\n", &j, j, *j);
printf("%x\t%x\t%x\t%d\n", &k, k, *k, ** k);
10
0x123aa8 i
name address contents
0x123aa8 0x123aab
j
0x123aab 0x123ab0
k

Algorithms and Data Structures
Dr. Andreas Nüchter
October 1, 2009
309
Linked Lists
• Flexible representation of dynamic sets
• Linear ordering of objects, where the ordering is