C++ Quick Syntax Reference Sheet & Standard Library Algorithmic Complexity

This quick reference cheat sheet provides a rapid lookup guide to modern C++ syntax, keywords, standard library containers, and mathematical time complexities.

STL Container Time Complexity Matrix

Container	Data Structure	Random Access `[]`	Front Insert/Delete	Back Insert/Delete	Search Complexity
`std::vector`	Contiguous Array	$O(1)$	$O(N)$	$O(1)$ Amortized	$O(N)$ linear / $O(log N)$ sorted
`std::deque`	Chunked Buffers	$O(1)$	$O(1)$	$O(1)$	$O(N)$
`std::list`	Doubly Linked List	$O(N)$ (No `[]`)	$O(1)$	$O(1)$	$O(N)$
`std::set / map`	Red-Black Tree	$O(log N)$ (map only)	$O(log N)$	$O(log N)$	$O(log N)$ Guaranteed
`std::unordered_map`	Hash Table	$O(1)$ Average	$O(1)$ Average	$O(1)$ Average	$O(1)$ Average ($O(N)$ worst)
`std::stack`	Adapter (Deque)	Not supported	Not supported	$O(1)$ Push/Pop	$O(1)$ Top only
`std::priority_queue`	Binary Max/Min Heap	Not supported	Not supported	$O(log N)$ Push/Pop	$O(1)$ Top element

Essential Modern C++ Syntax Snippets

// Smart Pointers
auto uPtr = std::make_unique<MyClass>(arg);   // Unique ownership (no copy)
auto sPtr = std::make_shared<MyClass>(arg);   // Shared ownership (ref count)

// Range-based for loop
for (const auto& item : container) { ... }    // Zero copy read-only

// Structured Bindings (C++17)
auto [key, value] = *mapIterator;

// Lambdas
auto isPositive = [](int x) { return x > 0; };

// Concepts (C++20)
template <std::integral T>
T gcd(T a, T b);

Frequently Asked Questions (FAQ) - Student & Interview Review

Q1. What is the best way to revise C++ before an exam or interview?

Bookmark this reference sheet! Review the STL container time complexity matrix, the 4 OOP pillars, smart pointer semantics, and the 4-stage compilation pipeline.

Q2. What is the Big-O complexity of searching in std::unordered_map vs std::map?

std::unordered_map provides average O(1) constant time lookups using hash buckets. std::map provides guaranteed O(log N) logarithmic time lookups using balanced Red-Black trees.