Post on 16-Aug-2020
Linked List Implementation
Mr. Mubashir AliLecturer (Dept. of Software Engineering)
mubashirali@lgu.edu.pkLahore Garrison University, Lahore
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Lecture 04
Previous Lecture
• Abstract List or List ADT
• Arrays
• Passing Arrays to Functions
• Searching Arrays: Linear VS Binary Search
• Lab Work
• 1st Submission
Mubashir Ali - Lecturer (Department of Software Engineering)
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Outline
1. Disadvantages of Physically Linear DataStructures
2. Treasure Hunt for Kids
3. Linked List
4. Traversal and Implementation
5. Array Based Implementation
Mubashir Ali - Lecturer (Department of Software Engineering)
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1. Disadvantages of Physically Linear Data Structures
• Fixed size
• Not flexible
• Insertion / deletion is difficult
• Always need boundary conditions
• etc
Mubashir Ali - Lecturer (Department of Software Engineering)
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Continued…
• Given an ordered-list:
– What happens when we add an element to the list?
– What happens when we delete an element from the list?
• In the array implementation, such cases require heavydata movement which is very costly.
• When we deal with linear or ordered-lists, it is in generally notrequired to have a random access to the elements. e.g., weusually don’t need to ask questions like: what is the 8thelement in the list?
• In most cases, the data is processed in a strictly sequentialorder.
• Therefore all that is required is the access to next element.
Mubashir Ali - Lecturer (Department of Software Engineering)
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Continued…
• In our previous mapping, the next element happensto be the element at the next index in the array.
• If we can some how tell where the next element isstored, we can eliminate this restriction of placingthe next element at the next physical location!
• This gives rise to the notion of logical adjacency asopposed to physical adjacency.
Mubashir Ali - Lecturer (Department of Software Engineering)
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Continued…
• In that case, in order to access the elements ofthe list, all we need is a starting point and somemechanism to from one element to the next.
• In other words, we need a starting point anda link form one element to the next.
Mubashir Ali - Lecturer (Department of Software Engineering)
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2. Treasure Hunt for Kids
In a party, clues are made up and scattered allover the house. Kids are divided into teams of 1to 4, depending on how many are at the party.Each clue leads to the next and at the end of thetrail is a treasure for the team, for example,chocolates, toys, etc.
Mubashir Ali - Lecturer (Department of Software Engineering)
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Continued…
• In that case, in order to access the elements ofthe list, all we need is a starting point and somemechanism to from one element to the next.
• In other words, we need a starting point and alink from one element to the next.
• We can only travel in the direction of the link.• We have a chain like structure and we can access
the elements in the chain by just following thelinks in the chain.
• Such an organization is known as a linked-list.
Mubashir Ali - Lecturer (Department of Software Engineering)
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3. Linked-lists
• This organization rids us from the requirement tomaintaining the logical as well as physical adjacency.
• Now all we need to maintain is the logical sequences andtwo logically adjacent elements need to not bephysically next to each other.
A linked list is a series of connected nodes
Each node contains at least
A piece of data (any type)
Pointer to the next node in the listHead: pointer to the first node
The last node points to NULL
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Key questions
• How do we represent a position in the list ?
• How do we iterate over the elements of a list ?
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Implementation
• We can implement this organization by storing the information and handle to the next element with the other data as follows:-
struct element {
handle next; // handle to next list element
data_type data;
};
handle head; // starting point - handle to first list element
head = // initialize head to - the end marker
Mubashir Ali - Lecturer (Department of Software Engineering)
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Linked-List Traversal
void traverse (handle head)
{
handle current = head;
while ( current != ) {
process data at current;
current = next field of current element
}
}
Mubashir Ali - Lecturer (Department of Software Engineering)
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Add an Element after current element
Mubashir Ali - Lecturer (Department of Software Engineering)
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Mubashir Ali - Lecturer (Department of Software Engineering)
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Fragile, Handle Links With Care
• If one link is broken, you loose access to all subsequent elements.
• What happens if you swap the following two lines in add:
next field of new element = next field of current; //step 2
next field of current = new_element; //step 3
• to
next field of current = new_element; //step 2
next field of new element = next field of current; //step 3
Mubashir Ali - Lecturer (Department of Software Engineering)
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Mubashir Ali - Lecturer (Department of Software Engineering)
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Delete an Element After Current Element
void delete (handle current)
{
handle temp = next field of current;
next field of current = next filed of next element
of current
// same as next field of
temp
discard temp
}
Mubashir Ali - Lecturer (Department of Software Engineering)
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Delete an Element After Current Element
Mubashir Ali - Lecturer (Department of Software Engineering)
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Garbage
• When all access paths to a data object are destroyedbut the data object continues to exist, the dataobject is said to be garbage.
• Garbage is a less serious but still troublesomeproblem. A data object that has become garbage tiesup storage that might otherwise be reallocated foranother purpose.
• A buildup of garbage can force the program toterminate prematurely because of lack of availablefree storage.
Mubashir Ali - Lecturer (Department of Software Engineering)
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Garbage
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Array Based Implementation
• Handle is the index of the next element in the array
struct node {
element_type data;// data
int next;// pointer to the next
} ;
Mubashir Ali - Lecturer (Department of Software Engineering)
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Array Based Implementation
class List {private:
int head;int available;int size;node * NodeList;
public:List (int s = 10); // constructor - default size =
10~List( ) { delete [ ] NodeList; } // destructorvoid processList();int search (int data);bool add (int data); // add in ascending ordervoid remove (int data); // delete node from the list
}
Mubashir Ali - Lecturer (Department of Software Engineering)
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Array Based Implementation
List::List(int s)
{
if (s <= 0) size = 10; else size = s;
nodeList = new node [size]; // create array
for (int i = 0; i < size-1; i++) // initialize
nodeList[i].next = i+1; // points to the next
nodeList [size-1].next = -1; // last node – there is no next
available = 0;
head = -1; // -1 is used as
}
Mubashir Ali - Lecturer (Department of Software Engineering)
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index 0 1 2 3 4 5 6 7 8 9
next 1 2 3 4 5 6 7 8 9 -1 available = 0
data - - - - - - - - - - head = -1
Mubashir Ali - Lecturer (Department of Software Engineering)
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Mubashir Ali - Lecturer (Department of Software Engineering)
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Initial state (available = 0, head = -1)
index 0 1 2 3 4 5 6 7 8 9
next 1 2 3 4 5 6 7 8 9 -1
data - - - - - - - - - -
Add 5 (available = 1, head = 0)
index 0 1 2 3 4 5 6 7 8 9
next -1 2 3 4 5 6 7 8 9 -1
data 5 - - - - - - - - -
Mubashir Ali - Lecturer (Department of Software Engineering)
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Add 7 (available = 2, head = 0)
index 0 1 2 3 4 5 6 7 8 9
next 1 -1 3 4 5 6 7 8 9 -1
data 5 7 - - - - - - - -
Add 8 (available = 3, head = 0)
index 0 1 2 3 4 5 6 7 8 9
next 1 2 -1 4 5 6 7 8 9 -1
data 5 7 8 - - - - - - -
Mubashir Ali - Lecturer (Department of Software Engineering)
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Add 6 (available = 4, head = 0)
index 0 1 2 3 4 5 6 7 8 9
next 3 2 -1 1 5 6 7 8 9 -1
data 5 7 8 6 - - - - - -
Add 2 (available = 5, head = 4)
index 0 1 2 3 4 5 6 7 8 9
next 3 2 -1 1 0 6 7 8 9 -1
data 5 7 8 6 2 - - - - -
Mubashir Ali - Lecturer (Department of Software Engineering)
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Add 7 (available = 1, head = 4)
index 0 1 2 3 4 5 6 7 8 9
next 3 5 -1 2 0 6 7 8 9 -1
data 5 - 8 6 2 - - - - -
Add 4 (available = 5, head = 4)
index 0 1 2 3 4 5 6 7 8 9
next 3 0 -1 2 1 6 7 8 9 -1
data 5 4 8 6 2 - - - - -
Mubashir Ali - Lecturer (Department of Software Engineering)
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Mubashir Ali - Lecturer (Department of Software Engineering)
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Delete 2 (available = 4, head = 1)
index 0 1 2 3 4 5 6 7 8 9
next 3 0 -1 2 5 6 7 8 9 -1
data 5 4 8 6 - - - - - -
Delete 8 (available = 2, head = 1)
index 0 1 2 3 4 5 6 7 8 9
next 3 0 4 -1 5 6 7 8 9 -1
data 5 4 - 6 - - - - - -
Summary
Disadvantages of Physically Linear DataStructures
Treasure Hunt for Kids
Linked List
Traversal and Implementation
Array Based Implementation
Mubashir Ali - Lecturer (Department of Software Engineering)
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References
you will be able to find course resources at
http://www.mubashirali.com/data-structures-algorithms/
Mubashir Ali - Lecturer (Department of Software Engineering)
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