Core Data Structures Flashcards
7 cards from real CodeSignal Technical Assessment practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Core Data Structures flashcards as text
Which data structure would you use to find the k-th largest element in a stream of numbers efficiently?
Answer: Min-heap of size k
A min-heap of size k keeps the k largest seen elements; its root is always the k-th largest.
What is the time complexity of deleting a node from the middle of a singly linked list, given a pointer directly to that node?
Answer: O(1)
With a direct pointer, you can copy the next node's data into the current node and delete the next node in O(1) time.
In a hash map using chaining, what is the worst-case time complexity for a lookup?
Answer: O(n)
If all n keys hash to the same bucket, the chain becomes a linked list of length n, requiring O(n) search.
Which property distinguishes a complete binary tree from a full binary tree?
Answer: A complete binary tree fills all levels left-to-right with the last level possibly incomplete; a full binary tree has every node with exactly 0 or 2 children
Complete binary trees fill each level left to right (last level may be partial), while full binary trees require every node to have 0 or 2 children.
What is a trie (prefix tree) primarily optimized for?
Answer: Fast prefix-based string lookups and autocomplete
A trie stores strings character by character, making prefix searches and autocomplete O(m) where m is the prefix length.
An undirected graph has 5 vertices and is fully connected (complete graph). How many edges does it have?
Answer: 10
A complete graph on n vertices has n(n-1)/2 edges; for n=5 that is 5×4/2 = 10.
What problem does a circular buffer (ring buffer) solve compared to a standard fixed-size queue?
Answer: It reuses memory by wrapping indices instead of shifting elements
A circular buffer uses modular arithmetic to wrap the head and tail pointers, reusing freed slots without shifting data.