The short answer
Python for most engineers. C++ only if you are targeting competitive programming roles, game/systems companies, or HFT firms that explicitly require it. Python lets you write 30–50% less code for the same algorithm, has built-in collections.deque, heapq, Counter, defaultdict, and sorted() that eliminate boilerplate. C++ is faster at runtime but runtime performance is almost never what interviewers care about — they care about algorithmic complexity.
Python advantages in interviews
Speed of writing: Python solutions are typically 30–50% shorter. Sorting is one line: sorted(arr, key=lambda x: x[1]). Heap: import heapq — heappush, heappop. Deque: from collections import deque. Frequency count: Counter(arr). Default dict: defaultdict(int). Tuple unpacking: a, b = b, a. List comprehensions eliminate filter/map boilerplate. Integer overflow does not exist in Python — integers are arbitrary precision, which removes an entire class of bugs. REPL-style iteration during the interview is fast.
C++ advantages in interviews
Runtime performance is 10–100x faster than Python, which matters for competitive programming but rarely for interviews. STL is powerful: std::priority_queue, std::map (ordered), std::unordered_map (hash), std::set, std::multiset. If the interviewer codes in C++ themselves, seeing idiomatic modern C++ (auto, range-for, structured bindings) signals seniority. For embedded, game, or systems roles: using C++ shows direct domain relevance. Some hard problems with tight time limits on LeetCode can TLE in Python but pass in C++.
When Python hurts you
Recursion depth: Python has a default limit of ~1000 frames. Deep DFS on large inputs hits RecursionError. Fix: sys.setrecursionlimit(10**6) or convert to iterative. Speed: heavy nested loops on 10^5 inputs can TLE. C++ or PyPy would pass. Precision: floating point arithmetic has the same issues as any language, but Python's decimal module is verbose. Multiprocessing: Python's GIL makes true parallelism impossible, but this is irrelevant for algorithm interviews. The recursion depth issue is the most common Python-specific bug in interviews — know the fix.
Java and other languages
Java is a solid third choice — verbose but familiar to many engineers coming from enterprise backgrounds. ArrayDeque, PriorityQueue, HashMap, and TreeMap cover all interview needs. The verbosity (Comparator boilerplate, generic syntax) costs time compared to Python. JavaScript/TypeScript: growing acceptance at smaller companies and frontend-focused roles, but no built-in heap/priority queue — you must implement one. Go: increasingly accepted at infrastructure companies. Rust: rarely accepted in interview settings — too much borrow-checker friction under time pressure. Recommendation: use the language you can write fastest with correct syntax under pressure.
Practical recommendation
If you know Python at a working level: use Python. Practice the standard imports so they are muscle memory: from collections import defaultdict, deque, Counter; import heapq. If you know C++ deeply (have used STL extensively): use C++ — the performance headroom is a safety net. If you know both equally: Python for the interview, C++ for competitive programming. Do NOT switch languages one week before your interview. Your speed in your primary language beats the raw performance of an unfamiliar language.