Algorithms Flashcards
7 cards from real HACKERRANK practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Algorithms flashcards as text
What is the output of `list(map(lambda x: x**2, [1, 2, 3, 4]))`?
Answer: [1, 4, 9, 16]
`map` applies the lambda squaring function to each element, producing [1, 4, 9, 16].
Which traversal of a binary tree visits nodes in the order: left subtree, root, right subtree?
Answer: In-order
In-order traversal follows left → root → right, which visits BST nodes in sorted order.
What Python built-in can find the greatest common divisor of two integers?
Answer: math.gcd(a, b)
`math.gcd(a, b)` computes the greatest common divisor using the Euclidean algorithm.
A sliding window of size k moves across an array of size n. What is the total number of windows?
Answer: n - k + 1
The first window starts at index 0 and the last at index n-k, giving n-k+1 total windows.
What does `heapq.nlargest(3, [5, 1, 8, 3, 9, 2])` return?
Answer: [9, 8, 5]
`heapq.nlargest(k, iterable)` returns the k largest elements in descending order.
Which sorting algorithm has the best average-case and worst-case time complexity of O(n log n)?
Answer: Merge Sort
Merge sort always divides and merges in O(n log n) regardless of input, unlike quicksort which degrades to O(n²).
In Python, what is the result of `[x for x in range(10) if x % 2 == 0]`?
Answer: [0, 2, 4, 6, 8]
The list comprehension filters range(10) for even numbers (remainder 0 when divided by 2).