Array

• A data structure that contains a list of elements accessed by an index– Array: a set of pairs (index and value)

– For each index, there is a value associated with that index.

• Arrays are generally a fixed size, which means you must specify the maximum size when the array is created

• Increasing the size of an array normally involves creating a new array of the desired size and copying the values from the old array to the new array

Array

• An array of size 5

String arr = new String[5];

Int nextIndex = 0;

• Set some of the values

arr[nextIndex ] = “Hi”

++nextIndex;

arr[nextIndex ] = “there”

++nextIndex;

arr[nextIndex ] = “Bob”

++nextIndex;

arr[nextIndex ] = “.”

++nextIndex;

Hi there Bob .

Array• Insert into the middle of a array

– Insert “Billy” between “there” and “Bob”

• Push “Bob” and “.” toward the end of the array to make space for “Bob” in element 2

insertIndex = 2;

for ( int i = nextIndex; i > = insertIndex; --i ) {

arr[i] = arr[i-1];

}

++nextIndex;

• Set the new value for element 2

arr[insertIndex] = “Billy”;

Hi there Bob .

Hi there Bob Bob .

Hi there Billy Bob .

Questions

• What is the complexity of “retrieve” in an array?

• What is the complexity of “store” in an array?

• What about insertion and deletion for ordered elements in an arrary?

Linked List

• A linked list is a data structure that contains a set of nodes linked with pointers.

• Singly-linked list has links in one direction. To the next node in the list.

• A doubly-linked list had links in both directions. To the next and previous nodes in the list.

Data

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Variable

Variable Data

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Data

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Data

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Data

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Data

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Data

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Data

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Linked List

• A Circularly-linked list has a complete cycles of links.

Variable Data

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Data

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Data

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Data

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Data

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Variable Data

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Data

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Linked List

• Insert at the end of a linked list

• Create new node

• Change the links to include the new node

Billy

Next

Hi

Next

Sentence there

Next

Bob

Next

.

Next

Linked List

• Insert into the middle of a linked list

• Create new node

• Change the links to include the new node

Hi

Next

Sentence there

Next

Bob

Next

.

Next

Billy

Next

Array versus Linked List

• Some operations are faster with one versus the other– Find element at position X – Array faster

– Find element Y at unknown position – Tie

– Insert element in the middle – Linked list faster

– Insert element at the end – Tie, if doubly-linked and circular, Array otherwise

– Insert element at the beginning – Linked list

• Arrays are (typically) a fixed size, linked lists are variable length

• Arrays are defined as holding a specific number of elements whether or not that many elements are currently in the array. Doing that wastes space