These tree, graph, and advanced problems come from [[u:/roadmaps/pattern-22|Pattern ]]. Solve them on LeetCode before the new problems below.
Clone Graph and Number of Islands test BFS/DFS fundamentals. For Clone Graph, use a hash map to track cloned nodes.
Kth Largest Element tests heap vs quickselect. Basic Calculator II tests stack-based expression parsing. Walkthroughs are linked.