CS 46B - Lecture 19

Pre-class reading

• Section 16.3

Implementing Stacks and Queues

• Stacks as linked lists
• Stacks as array lists
• Queues as linked lists
• Queues as circular arrays

Stacks as Linked Lists

• Sequence of nodes
• Singly linked list
• push adds a new node
• pop removes a node
• Both are O(1)

Lecture 19 Clicker Question 1

Where should the nodes be added/removed for maximum efficiency?

1. push adds before first, pop removes last
2. push adds before first, pop removes first
3. push adds after last, pop removes last
4. push adds after last, pop removes first

Stacks as Array Lists

• Use buffer that can fill up
• Relocate buffer, doubling its size when it is full
• push adds element to buffer, increments size
• pop returns buffer element, decrements size
• Both are O(1)+

Lecture 19 Clicker Question 2

Where should the elements be added/removed for maximum efficiency?

1. push adds before first, pop removes last
2. push adds before first, pop removes first
3. push adds after last, pop removes last
4. push adds after last, pop removes first

Queues as Linked Lists

• Sequence of nodes
• Singly linked list
• add adds a new node
• remove removes a node
• Both are O(1)

Lecture 19 Clicker Question 3

Where should the nodes be added/removed for maximum efficiency?

1. add adds before first, remove removes last
2. add adds before first, remove removes first
3. add adds after last, remove removes last
4. add adds after last, remove removes first

Queues as Circular Arrays

• Use buffer that can fill up
• Index for head, tail
• Occupied area can “wrap around”
• add/remove are O(1)+

Lecture 19 Clicker Question 4

Assume the buffer has size 10. What is its contents after these operations?

for (i = 1; i <= 8; i++) q.add(i);
for (i = 1; i <= 4; i++) q.remove();
for (i = 1; i <= 8; i++) q.add(i);
for (i = 1; i <= 4; i++) q.remove();

1. 1 2 3 4 5 6 7 8
2. 3 4 5 6 7 8 7 8 1 2
3. 3 4 5 6 7 8 0 0 1 2
4. Something else