The document discusses stacks and queues, focusing on the stack as a linear structure with LIFO (last in, first out) operations. It explains basic stack operations such as push and pop, and their implementations in Python. Additionally, it highlights applications of stacks, including reversing strings and converting infix expressions to postfix notation.

1. Data Structures-II Stack
& Queues

2. Stacks
• Stack is a linear structure in which insertion and
deletion occur in LIFO pattern
• The end of the stack in which these operations
occur is called top of stack
• Any data can inserted or deleted only through
the top
• Deletion is called pop and insertion is called
push
• Some other terminologies used with stack are:
peek, overflow, underflow

3. Implementation of Stacks in Python
• Peek
• <stack>[top]
• Push
• <stack>.append(<item>)
• Pop
• <stack>.pop()

4. Stack Implementation in Python

5. Applications of stack
• To reverse a String: When we
push every letter of a string till
the last character and pop them
back we get the string in
reverse
• For polish notation: Stack plays
a vital role in solving complex
arithmetic expressions in any
high-level language. For this
stack is used to convert an
expression in infix notation to
postfix and vice versa.
K
C
A
T
S

6. Infix topostfix

7. postfix Solve- 60,6,/,5,2,*,5,-,+

8. Infixtopostfix

9. Solving Postfix