Stacks - DSA Notes 📝

🎯 Learning Goals

• How are Stacks implemented?
• What are the time complexities?

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🧠 Key Concepts (aka My Notes)

Stacks

• Dynamic arrays are already Stacks.
• LIFO (Last In is the First Out)
• There should be a pointer for the last element in the array.

Push

• Appending an element to the end of a dynamic array

⌚ Time Complexity is O(1).

Push

• Removing an element to the end of a dynamic array
• It is wise to check if the stack is empty before popping

⌚ Time Complexity is O(1).

Peek

• Returning an element to the end of a dynamic array

⌚ Time Complexity is O(1).

⌚ Time Complexity for Stacks

Operation	Big-O
Push	O(1)
Pop	O(1)
Peek	O(1)

💪 LeetCode Problems

• 155. Min Stack (Link)
• 20. Valid Parentheses (Link)