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63 lines
1.6 KiB
Plaintext
63 lines
1.6 KiB
Plaintext
---
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title: Stack
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description: 'Items are added and removed from one end, so the last item added is the first item removed.'
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hidden: true
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---
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A stack works like a stack of plates in a cafeteria. You add new plates on top. When you need a plate, you take from the top. The last plate you added is the first one you remove.
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This is **Last-In-First-Out (LIFO)**. The most recent item goes out first.
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## Core Stack Operations
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A stack has two fundamental operations:
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- **Push**: add an item to the top of the stack
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- **Pop**: remove the item at the top of the stack
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Some stacks have additional operations:
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- **Peek**: get the item at the top of the stack without removing it
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- **IsEmpty**: check if the stack is empty
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```python
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# Using Python list as a stack
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stack = []
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# Push elements
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stack.append(10)
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stack.append(20)
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stack.append(30)
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# Stack: [10, 20, 30] (30 is on top)
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# Pop element
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top = stack.pop() # Returns 30
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# Stack: [10, 20]
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# Peek at top
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if stack:
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top_element = stack[-1] # Returns 20 without removing
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```
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Python lists provide `append()` for pushing and `pop()` for popping. The `peek()` method is not built-in, but you can implement it yourself.
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## Last in, First out
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The defining characteristic of a stack is LIFO order. Whatever you put in last comes out first. This is different from a queue, which is First-In-First-Out (FIFO).
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Add items: A, B, C
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- Stack: [A, B, C] (C on top)
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Remove items:
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- First pop: C
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- Second pop: B
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- Third pop: A
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The order reverses. Items come out in the opposite order they went in.
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