All revision cards
Split the text into words, normalize if needed, and increment counts in a dictionary. Python collections.Counter is great, but interviewers may ask for the manual version first.
Return a frequency map for the words in a sentence.
Move one pointer one step and another pointer two steps at a time. If they ever meet, there is a cycle; if the fast pointer reaches the end, the list is acyclic.
Return whether a linked list contains a cycle.
Track only the previous two numbers and iterate until you reach n. This keeps the solution clear and avoids exponential recursion.
Return the nth Fibonacci number.
Walk the list once, keep a set of seen values, and add repeated values into a duplicate set. Convert to a sorted list if stable output helps.
Return the duplicate values from a list of integers.
Advance a slow pointer by one step and a fast pointer by two steps. When the fast pointer reaches the end, the slow pointer will be at the middle.
Return the middle node of a singly linked list.
Build a frequency map for the characters, then iterate through the string a second time to return the first character whose count is one.
Return the first character in a string that appears exactly once, or an empty string if none exists.
Use a dictionary keyed by the sorted characters of each word, then append each word into the matching bucket.
Group words that are anagrams of each other and return the grouped lists.
Track the best result when including or excluding the current house. A rolling two-variable DP solution keeps the implementation compact.
Return the maximum amount you can rob from houses without robbing adjacent houses.
Wrap a `deque` inside a small class so enqueue uses `append`, dequeue uses `popleft`, and peek reads the leftmost item without removing it.
Implement a queue with enqueue, dequeue, and peek operations.
Convert both arrays to sets, intersect them, and sort the result if you want deterministic output for testing or interviews.
Return the unique values that appear in both arrays.