Backtracking

Problem	Complexity	Key Pattern
Combination Sum	O(2^target) (bounded by target / min(candidates))	Partition into target — "all combinations summing to T", "coin change
N Queens	O(n!) (with pruning)	Constraint placement — "place N items with mutual exclusion constraints",
Permutations	O(n * n!)	All orderings — "generate all permutations", "all arrangements",
Subsets	O(n * 2^n)	Power set / feature combinations — "generate all subsets", "all