C++ Interview Guide

A practical C++ reference for coding interviews — STL containers, algorithms, complexity analysis, and idiomatic patterns.

Why This Guide

C++ is popular in interviews because of its explicit control over memory, rich STL, and predictable performance. But the language is also huge — this guide cuts it down to what you actually need for a technical interview: fast I/O, the right STL container for the job, the algorithms that handle 80% of problems, and the patterns you'll see over and over.

Every section includes time and space complexity so you can justify your choices during the interview.

Contents

#	File	Topic
1	01-cpp-essentials	Modern C++ essentials — I/O optimization, auto, range-for, lambdas, structured bindings, pair/tuple, common gotchas
2	02-stl-containers	vector, deque, list, string, stack, queue, priority_queue, set/map (ordered), unordered_set/unordered_map, bitset — with complexity tables
3	03-stl-algorithms	sort, binary_search, lower_bound/upper_bound, reverse, rotate, unique, accumulate, count, find, min_element/max_element, partition, next_permutation — with complexity
4	04-cpp-interview-patterns	Two pointers, sliding window, prefix sums, monotonic stack, BFS/DFS, binary search on answer, DP — idiomatic C++

Quick Reference — Pick the Right Container

Need	Container	Access	Insert	Search
Dynamic array	vector	O(1)	O(1) amortized back	O(n)
Queue both ends	deque	O(1)	O(1) front/back	O(n)
Sorted, unique	set	—	O(log n)	O(log n)
Sorted, key→value	map	O(log n)	O(log n)	O(log n)
Hash, unique	unordered_set	—	O(1) avg	O(1) avg
Hash, key→value	unordered_map	O(1) avg	O(1) avg	O(1) avg
LIFO	stack	top only	O(1)	—
FIFO	queue	front/back	O(1)	—
Max/min priority	priority_queue	top only	O(log n)	—
Bit flags	bitset	O(1)	—	—

Quick Reference — Boilerplate

#include <bits/stdc++.h>
using namespace std;

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);

    // your solution here

    return 0;
}

Revision Checklist

• [ ] Memorize complexity of every STL container operation
• [ ] Practice lower_bound / upper_bound — know they return iterators
• [ ] Know when to use unordered_map vs map (hash collisions, iteration order)
• [ ] Understand when iterator invalidation happens (vector on realloc, erase)
• [ ] Know the 3 ways to sort (ascending, descending, custom comparator)
• [ ] Be able to write BFS/DFS from scratch in under 3 minutes
• [ ] Know the bits/stdc++.h + fast I/O boilerplate cold

Cross-References

Topic	Where
DSA problems with C++ solutions	Amazon Prep DSA
Graph algorithms (DFS, BFS, Dijkstra)	Temple Prep Graphs
DP, Arrays, Strings, Trie	Temple Prep DSA Core