You've worked through tree, graph, and DP problems.
Grid DFS/BFS finds connected components (Number of Islands). Visit each cell once.
Topological sort detects cycles and orders dependencies (Course Schedule). Use Kahn's or DFS coloring.
BFS by level solves per-level queries on trees (Right Side View). Take the last node at each depth.
BST property lets you make binary decisions (LCA of BST). time.
DP handles overlapping subproblems (Word Break, Coin Change). Define state, base case, transition.
Min-heap merges sorted sequences in time and space.