CSE1301 Computer Programming: Lecture 33 Linked Lists.

CSE1301 Computer Programming:

Lecture 33Linked Lists

Topics

• Linked list

• List element

• Searching a linked list

Recall: Sorted List

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Recall: Sorted List

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Ann

Recall: Sorted List

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Ann

Recall: Sorted List

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Ann

Dave

Recall: Sorted List

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Ann Dave

Recall: Sorted List

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Ann Dave

Humphry

Recall: Sorted List

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Ann Dave Humphry

Recall: Sorted List

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Ann Dave Humphry

Ben

Recall: Sorted List

0 1 2 3 4

Ann Dave Humphry

Ben

Recall: Sorted List

0 1 2 3 4

Ann Dave Humphry

Ben

Recall: Sorted List

0 1 2 3 4

Ann Dave HumphryBen

Recall: Sorted List

0 1 2 3 4

Ann Dave HumphryBen

Q: Is there an alternative way to implement a sorted list?

A: Linked List

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Ann Dave Humphry

Ben

First

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Ann Dave Humphry

Ben

First

0 1 2 3 4

Ann Dave Humphry

Ben

First

0 1 2 3 4

Ann Dave Humphry

Ben

First

0 1 2 3 4

Ann Dave Humphry

First

Ben

0 1 2 3 4

Ann Dave Humphry Ben

First

0 1 2 3 4

Ann Dave Humphry Ben

First

0 1 2 3 4

Ann Dave Humphry Ben

First

Amy

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Ann Dave Humphry Ben

First

Amy

0 1 2 3 4

Ann Dave Humphry Ben

First

Amy

0 1 2 3 4

Ann Dave Humphry Ben

First

Amy

0 1 2 3 4

first element

index of next element

item

invalid index (eg. -1)

Linked List

• Uses an array to form a sorted list

• Each element has a link to the next item

8 2 9 5 34

first 10 1 2 3 54

5 34 02 -1

List Element

struct ListElementRec

{

int item;

int next;

};

typedef struct ListElementRec ListElement;

2item

next 5

What will a program have?

• An array of these structs ListElement list[maxListLength];

• A variable to store the position of the first element of the list int first;

• The last element in the list must contain a non valid integer in its next fieldconst int END = -1;

Accessing list items

• First element (a struct) list[first];

• First item in list list[first].item;

• Index of next element list[first].next;

Accessing list items

• Next item in list

int index;

list[list[index].next].item; index 4

8 2 9 5 34

first 10 1 2 3 54

5 34 02 END

Searching in a linked list

• See Algorithm in Lecture Notes

• Example: Trace values for:index

linkedList[index].item

linkedList[index].next

Summary

• In a linked list, list elements don't have to be ordered in the array itself.

• A second field in the list element structure, "next", maintains the list ordering.

• Next lecture: adding and deleting from a linked list