Computer Notes - Data Structures - 2

8/3/2019 Computer Notes - Data Structures - 2

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Class No.02

Data Structures

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Implementing Lists

We have designed the interface for the List; wenow must consider how to implement thatinterface.

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Implementing Lists

We have designed the interface for the List; wenow must consider how to implement thatinterface.

Implementing Lists using an array: for example,the list of integers (2, 6, 8, 7, 1) could berepresented as:

A

6 8 7 11 2 3 4 5

2 current3

size5

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List Implementation

add(9); current position is 3. The new list would thusbe: (2, 6, 8, 9, 7, 1)

We will need to shifteverything to the right of 8 oneplace to the right to make place for the new element 9.

current

3

size

5step 1: A

6 8 7 1

1 2 3 4 5

2

6

current

4

size

6step 2: A 6 8 7 1

1 2 3 4 5

2

6

9

notice: current points

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Implementing Lists

next():

current

4

size

6A

6 8 7 1

1 2 3 4 5

2

6

9

5



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Implementing Lists

There are special cases for positioning thecurrent pointer:

a. past the last array cell

b. before the first cell



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Implementing Lists

There are special cases for positioning thecurrent pointer:

a. past the last array cellb. before the first cell

We will have to worry about these when we

write the actual code.



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Implementing Lists

remove(): removes the element at the currentindex

current

5

size

6

A 6 8 1

1 2 3 4 5

2

6

9

5

Step 1:

current

5

size

5A 6 8 1

1 2 3 4 5

2 9Step 2:



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Implementing Lists

remove(): removes the element at the currentindex

We fill the blank spot left by the removal of 7 byshifting the values to the right of position 5 overto the left one space.

current

5

size

5A 6 8 1

1 2 3 4 5

2 9Step 2:

current

5

size

6

A 6 8 1

1 2 3 4 5

2

6

9

5

Step 1:


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Implementing Lists

find(X): traverse the array until X is located.

int find(int X){

int j;

for(j=1; j < size+1; j++ )if( A[j] == X ) break;

if( j < size+1 ) { // found Xcurrent = j; // current points to where X found

return 1; // 1 for true}return 0; // 0 (false) indicates not found

} http://ecomputernotes.com


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Implementing Lists

Other operations:

get() return A[current];

update(X) A[current] = X;length() return size;

back() current--;

start()

current = 1;end() current = size;



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Analysis of Array Lists

add

we have to move every element to the right ofcurrent to make space for the new element.

Worst-case is when we insert at the beginning; wehave to move every element right one place.

Average-case: on average we may have to movehalf of the elements



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Analysis of Array Lists

remove Worst-case: remove at the beginning, must shift all

remaining elements to the left. Average-case: expect to move half of the elements.

find Worst-case: may have to search the entire array Average-case: search at most half the array.

Other operations are one-step.



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List Using Linked Memory

Various cells of memory are not allocatedconsecutively in memory.



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Not enough to store the elements of the list.



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With arrays, the second element was right nextto the first element.



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Now the first element must explicitlytell us

where to look for the second element.



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Now the first element must explicitlytell us

where to look for the second element. Do this by holding the memory address of the

second element



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Linked List

Create a structure called a Node.

object next

The objectfield will hold the actual list element.

The nextfield in the structure will hold the

starting location of the next node. Chain the nodes together to form a linked list.



20/24

Linked List

Picture of our list (2, 6, 7, 8, 1) stored as alinked list:

2 6 8 7 1

head

current

size=5



21/24

Linked List

Note some features of the list:

Need a headto point to the first node of the list.

Otherwise we wont know where the start of the

list is.



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Linked List




list is.

The currenthere is a pointer, not an index.



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Linked List




list is.

The currenthere is a pointer, not an index.

The next field in the last node points to nothing.

We will place the memory address NULL whichis guaranteed to be inaccessible.



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Linked List

Actual picture in memory:1051

1052

1055

1059

10601061

1062

1063

1064

1056

1057

1058

1053

1054 2

6

8

7

1

1051

1063

1057

1060

0

head 1054

1063current

2 6 8 7 1

head

current

1065

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Computer Notes - Data Structures - 2