Here are my slides for my preparation class for possible Master students in Electrical Engineering and Computer Science (Specialization in Computer Science)... for the entrance examination here at Cinvestav GDL

1. Data Structures
Linear List Array Representation
Andres Mendez-Vazquez
May 6, 2015
1 / 24

2. Images/cinvestav-
Outline
1 Linear List Array Representation
Operations in Array List
2 Dynamic Arrays
How much we need to expand it...
A Strategy for it
Analysis
2 / 24

3. Images/cinvestav-
How do we implement the ADT List?
In our first representation will use an array
Use a one-dimensional array element[]:
a b c d e - - - -
0 1 2 3 4 5 6 7 8
The previous array
A representation of L = (a, b, c, d, e) using position i in element[i].
3 / 24

4. Images/cinvestav-
How do we implement the ADT List?
In our first representation will use an array
Use a one-dimensional array element[]:
a b c d e - - - -
0 1 2 3 4 5 6 7 8
The previous array
A representation of L = (a, b, c, d, e) using position i in element[i].
3 / 24

5. Images/cinvestav-
Where to map in the array
Right To Left Mapping
- - - - e d c b a
Mapping That Skips Every Other Position
a - b - c - d - e - -
Wrap Around Mapping
d e - - - - - - a b c
4 / 24

6. Images/cinvestav-
Where to map in the array
Right To Left Mapping
- - - - e d c b a
Mapping That Skips Every Other Position
a - b - c - d - e - -
Wrap Around Mapping
d e - - - - - - a b c
4 / 24

7. Images/cinvestav-
Where to map in the array
Right To Left Mapping
- - - - e d c b a
Mapping That Skips Every Other Position
a - b - c - d - e - -
Wrap Around Mapping
d e - - - - - - a b c
4 / 24

8. Images/cinvestav-
Representation Used In Text
Something Notable
a b c d e - - - -
0 1 2 3 4 5 6 7 8
Size=5
Thus
1 Put element i of list in element[i].
2 Use a variable size to record current number of elements
5 / 24

9. Images/cinvestav-
Representation Used In Text
Something Notable
a b c d e - - - -
0 1 2 3 4 5 6 7 8
Size=5
Thus
1 Put element i of list in element[i].
2 Use a variable size to record current number of elements
5 / 24

10. Images/cinvestav-
Code
Our Implementation
p u b l i c c l a s s S i m p l e A r r a y L i s t <Item> implements
L i n e a r L i s t <Item >{
// p r i v a t e elements of implementation
p r o t e c t e d Item element [ ] ;
p r o t e c t e d i n t s i z e ;
p r o t e c t e d f i n a l s t a t i c i n t DEFAULT_SIZE = 10;
// C o n s t r u c t o r s
p u b l i c S i m p l e A r r a y L i s t (){
t h i s . s i z e = 0;
t h i s . element = ( Item [ ] ) new Object [ t h i s . DEFAULT_SIZE ] ;
}
p u b l i c S i m p l e A r r a y L i s t ( i n t NewSize ){
t h i s . s i z e = 0;
t h i s . element = ( Item [ ] ) new Object [ NewSize ] ;
}
6 / 24

11. Images/cinvestav-
Data Type Of Array element[]
First than anything
Data type of list elements is unknown.
Thus, we used the genericity of Object
1 Then, we use element[] to be of data type Object.
2 Then, we cast to the new “Item.”
However
You cannot put elements of primitive data types (int, float, double, char,
etc.) into our linear lists.
7 / 24

12. Images/cinvestav-
Data Type Of Array element[]
First than anything
Data type of list elements is unknown.
Thus, we used the genericity of Object
1 Then, we use element[] to be of data type Object.
2 Then, we cast to the new “Item.”
However
You cannot put elements of primitive data types (int, float, double, char,
etc.) into our linear lists.
7 / 24

13. Images/cinvestav-
Data Type Of Array element[]
First than anything
Data type of list elements is unknown.
Thus, we used the genericity of Object
1 Then, we use element[] to be of data type Object.
2 Then, we cast to the new “Item.”
However
You cannot put elements of primitive data types (int, float, double, char,
etc.) into our linear lists.
7 / 24

14. Images/cinvestav-
Data Type Of Array element[]
First than anything
Data type of list elements is unknown.
Thus, we used the genericity of Object
1 Then, we use element[] to be of data type Object.
2 Then, we cast to the new “Item.”
However
You cannot put elements of primitive data types (int, float, double, char,
etc.) into our linear lists.
7 / 24

15. Images/cinvestav-
Outline
1 Linear List Array Representation
Operations in Array List
2 Dynamic Arrays
How much we need to expand it...
A Strategy for it
Analysis
8 / 24

16. Images/cinvestav-
Operations: Add
Add/Remove an element
a b c d e - - - -
0 1 2 3 4 5 6 7 8
Size=5
add(1,g)
a g b c d e - - -
0 1 2 3 4 5 6 7 8
Size=6
9 / 24

17. Images/cinvestav-
Operations: Add
Add/Remove an element
a b c d e - - - -
0 1 2 3 4 5 6 7 8
Size=5
add(1,g)
a g b c d e - - -
0 1 2 3 4 5 6 7 8
Size=6
9 / 24

18. Images/cinvestav-
Code
Our Implementation
p u b l i c void add ( i n t index , Item myobject ){
// I n i t i a l V a r i a b l e s
i n t i ;
// Always check f o r p o s s i b l e e r r o r s
i f ( t h i s . s i z e == element . len ght ){
System . out . p r i n t l n ( " L i s t ␣ does ␣ not ␣ have ␣ space " ) ;
System . e x i t ( 0 ) ;
}
i f ( index <0 | | index >t h i s . s i z e ){
System . out . p r i n t l n ( " Index ␣ out ␣ of ␣bound " ) ;
System . e x i t ( 0 ) ;
}
// S h i f t p o s t i i o n s as n e c e s s a r y
f o r ( i = t h i s . s i z e ; i >index ; i −−)
element [ i +1]=element [ i ] ;
// copy element i n t o c o n t a i n e r
element [ i +1]=myobject ;
}
10 / 24

19. Images/cinvestav-
Operations: Get
Here
We have
a b c d e - - - -
0 1 2 3 4 5 6 7 8
Size=5
get(3)
It will return “d”.
The code is simple
11 / 24

20. Images/cinvestav-
Operations: Get
Here
We have
a b c d e - - - -
0 1 2 3 4 5 6 7 8
Size=5
get(3)
It will return “d”.
The code is simple
11 / 24

21. Images/cinvestav-
Operations: Get
Here
We have
a b c d e - - - -
0 1 2 3 4 5 6 7 8
Size=5
get(3)
It will return “d”.
The code is simple
p u b l i c Item get ( i n t index ){
// Check always
i f ( t h i s . s i z e == 0) r e t u r n n u l l ;
i f ( index <0 | | index >t h i s . s i z e −1){
System . out . p r i n t l n ( " Index ␣ out ␣ of ␣bound " ) ;
System . e x i t ( 0 ) ;
}
r e t u r n element [ index ]
}
11 / 24

22. Images/cinvestav-
You can implement the rest
Yes
Part of your homework!!!
12 / 24

23. Images/cinvestav-
Now, we have a common problem
Because
We do not know how many elements will be stored at the list.
We use
An initial length and dynamically increase the size as needed.
13 / 24

24. Images/cinvestav-
Now, we have a common problem
Because
We do not know how many elements will be stored at the list.
We use
An initial length and dynamically increase the size as needed.
13 / 24

25. Images/cinvestav-
Example
Example
Length of array element[] is 6:
a b c d e f
First create a new and larger array
NewArray = (Item[]) new Object[12]
- - - - - - - - - - - -
Now copy the new elements into the new array!!!
System.arraycopy(element, 0, newArray, 0, element.length);
a b c d e f - - - - - -
14 / 24

26. Images/cinvestav-
Example
Example
Length of array element[] is 6:
a b c d e f
First create a new and larger array
NewArray = (Item[]) new Object[12]
- - - - - - - - - - - -
Now copy the new elements into the new array!!!
System.arraycopy(element, 0, newArray, 0, element.length);
a b c d e f - - - - - -
14 / 24

27. Images/cinvestav-
Example
Example
Length of array element[] is 6:
a b c d e f
First create a new and larger array
NewArray = (Item[]) new Object[12]
- - - - - - - - - - - -
Now copy the new elements into the new array!!!
System.arraycopy(element, 0, newArray, 0, element.length);
a b c d e f - - - - - -
14 / 24

28. Images/cinvestav-
Example
Finally, rename new array
element = NewArray;
element[0]−→ a b c d e f - - - - - -
15 / 24

29. Images/cinvestav-
Outline
1 Linear List Array Representation
Operations in Array List
2 Dynamic Arrays
How much we need to expand it...
A Strategy for it
Analysis
16 / 24

30. Images/cinvestav-
First Attempt
What if you use the following policy?
At least 1 more than current array length.
Thus
What would be the cost of all operations?
Generate a new array.
Copy all the items to it.
insert the new element at the end.
17 / 24

31. Images/cinvestav-
First Attempt
What if you use the following policy?
At least 1 more than current array length.
Thus
What would be the cost of all operations?
Generate a new array.
Copy all the items to it.
insert the new element at the end.
17 / 24

32. Images/cinvestav-
First Attempt
What if you use the following policy?
At least 1 more than current array length.
Thus
What would be the cost of all operations?
Generate a new array.
Copy all the items to it.
insert the new element at the end.
17 / 24

33. Images/cinvestav-
First Attempt
What if you use the following policy?
At least 1 more than current array length.
Thus
What would be the cost of all operations?
Generate a new array.
Copy all the items to it.
insert the new element at the end.
17 / 24

34. Images/cinvestav-
First Attempt
What if you use the following policy?
At least 1 more than current array length.
Thus
What would be the cost of all operations?
Generate a new array.
Copy all the items to it.
insert the new element at the end.
17 / 24

35. Images/cinvestav-
What if we do n insertions?
We finish with something like this
1 First Insertion: Creation of the List ⇒ Cost = 1.
2 Second Insertion Cost = 2.
3 Third Insertion Cost = 3
4 etc!!!
Thus, we have
Ok
Not a good idea!!!
18 / 24

36. Images/cinvestav-
What if we do n insertions?
We finish with something like this
1 First Insertion: Creation of the List ⇒ Cost = 1.
2 Second Insertion Cost = 2.
3 Third Insertion Cost = 3
4 etc!!!
Thus, we have
Ok
Not a good idea!!!
18 / 24

37. Images/cinvestav-
What if we do n insertions?
We finish with something like this
1 First Insertion: Creation of the List ⇒ Cost = 1.
2 Second Insertion Cost = 2.
3 Third Insertion Cost = 3
4 etc!!!
Thus, we have
Ok
Not a good idea!!!
18 / 24

38. Images/cinvestav-
What if we do n insertions?
We finish with something like this
1 First Insertion: Creation of the List ⇒ Cost = 1.
2 Second Insertion Cost = 2.
3 Third Insertion Cost = 3
4 etc!!!
Thus, we have
Ok
Not a good idea!!!
18 / 24

39. Images/cinvestav-
What if we do n insertions?
We finish with something like this
1 First Insertion: Creation of the List ⇒ Cost = 1.
2 Second Insertion Cost = 2.
3 Third Insertion Cost = 3
4 etc!!!
Thus, we have
1 + 2 + 3 + · · · + n =
n (n + 1)
2
= O n2
(1)
Ok
Not a good idea!!!
18 / 24

40. Images/cinvestav-
What if we do n insertions?
We finish with something like this
1 First Insertion: Creation of the List ⇒ Cost = 1.
2 Second Insertion Cost = 2.
3 Third Insertion Cost = 3
4 etc!!!
Thus, we have
1 + 2 + 3 + · · · + n =
n (n + 1)
2
= O n2
(1)
Ok
Not a good idea!!!
18 / 24

41. Images/cinvestav-
Outline
1 Linear List Array Representation
Operations in Array List
2 Dynamic Arrays
How much we need to expand it...
A Strategy for it
Analysis
19 / 24

42. Images/cinvestav-
A better strategy
Dynamic Array
To avoid incurring the cost of resizing many times, dynamic arrays resize
by an amount a.
In our example we double the size, a = 2
20 / 24

43. Images/cinvestav-
A better strategy
Dynamic Array
To avoid incurring the cost of resizing many times, dynamic arrays resize
by an amount a.
In our example we double the size, a = 2
Item NewArray [ ] ;
i f ( t h i s . s i z e == element . len ght ){
// Resize the c a p a c i t y
NewArray = ( Item [ ] ) new Object [ 2*this.size ]
f o r ( i n t i =0; i < s i z e ; i ++){
NewArray [ i ]= element [ i ] ;
}
element = NewArray ;
}
20 / 24

44. Images/cinvestav-
Space Complexity
Every time an insertion triggers a doubling of the array
Thus, space wasted in the new array:
Space Wasted = Old Lenght − 1 (2)
Remember: We double the array and insert!!!
Thus, the average space wasted is
Θ (n) (3)
21 / 24

45. Images/cinvestav-
Space Complexity
Every time an insertion triggers a doubling of the array
Thus, space wasted in the new array:
Space Wasted = Old Lenght − 1 (2)
Remember: We double the array and insert!!!
Thus, the average space wasted is
Θ (n) (3)
21 / 24

46. Images/cinvestav-
For example, we have the following
A trade-off between time and space
You have and average time for insertion is 2
2−1 .
In addition, an upper bound for the wasted cells in the array is
(2 − 1) n − 1 = n − 1.
Actually a more general term of expansion, a
Thus, we have:
Average time for insertion is a
a−1 .
An upper bound for the wasted cells in the array is
(a − 1) n − 1 = an − n − 1.
Different languages use different values
Java, a = 3
2 .
Python, a = 9
8
22 / 24

47. Images/cinvestav-
For example, we have the following
A trade-off between time and space
You have and average time for insertion is 2
2−1 .
In addition, an upper bound for the wasted cells in the array is
(2 − 1) n − 1 = n − 1.
Actually a more general term of expansion, a
Thus, we have:
Average time for insertion is a
a−1 .
An upper bound for the wasted cells in the array is
(a − 1) n − 1 = an − n − 1.
Different languages use different values
Java, a = 3
2 .
Python, a = 9
8
22 / 24

48. Images/cinvestav-
For example, we have the following
A trade-off between time and space
You have and average time for insertion is 2
2−1 .
In addition, an upper bound for the wasted cells in the array is
(2 − 1) n − 1 = n − 1.
Actually a more general term of expansion, a
Thus, we have:
Average time for insertion is a
a−1 .
An upper bound for the wasted cells in the array is
(a − 1) n − 1 = an − n − 1.
Different languages use different values
Java, a = 3
2 .
Python, a = 9
8
22 / 24

49. Images/cinvestav-
Outline
1 Linear List Array Representation
Operations in Array List
2 Dynamic Arrays
How much we need to expand it...
A Strategy for it
Analysis
23 / 24

50. Images/cinvestav-
We have the following final analysis
Amortized Analysis Vs. Classic
Array Classic Analysis Dynamic Array
Amortized Analysis
Indexing O (1) O (1)
Search O (n) O (n)
Add/Remove O (n) O (n)
Space Complexity O (n) O (n)
24 / 24