Cheat Sheet

Stack Cheat Sheet

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What is Stack?

Understand LIFO data structure and its applications in parsing and backtracking.

Trigger Words

When you see these in a problem, think Stack:

valid parentheses stack min stack evaluate reverse polish notation generate parentheses daily temperatures car fleet largest rectangle in histogram

Template Code

def isValid(s: str) -> bool:
    stack = []
    mapping = {&#039;)': '(', '}': '{', ']': '['}
    
    for char in s:
        if char in mapping:  # Closing bracket
            if not stack or stack[-1] != mapping[char]:
                return False
            stack.pop()
        else:  # Opening bracket
            stack.append(char)
    
    return len(stack) == 0

Complexity

Typical Time	`O(n)`
Typical Space	`O(n)`

Common Variations

Basic Stack
Stack with constraints
Optimized Stack

Practice Problems

Valid Parentheses medium Min Stack medium Evaluate Reverse Polish Notation medium Generate Parentheses medium Daily Temperatures medium

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Practice Stack

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