Meta's most-asked coding categories by frequency:
Arrays and strings (%). Two Sum, valid parentheses, substring problems.
Trees (%). Vertical order traversal, serialization, LCA.
Graphs (%). Number of islands, clone graph, shortest path.
Sorting and searching (%). Merge intervals, kth largest element.
Stacks and queues (%). Parentheses matching, monotonic stack.
Meta rarely asks dynamic programming at E4. DP appears more at E5+.