Two pointers, sliding window, prefix sum, hashing, binary search patterns.
Reverse list, cycle detection (Floyd), merge sorted lists, middle node, k-th from end.
Monotonic stack, next greater element, valid parentheses, BFS queue usage.
DFS traversals, BFS levels, height/diameter, LCA, validate BST, recursion templates.
BFS/DFS, topological sort, shortest path basics, connected components, union-find.
Subsets, permutations, N-Queens, combination sum, pruning strategy.
1D/2D state design, transition formula, base cases, memoization vs tabulation.
Big-O estimation, worst vs average case, trade-offs, optimization techniques.