backtracking (systematic trial with undo) builds solutions incrementally, abandoning paths that can't lead to valid solutions. You use it when generating all combinations, permutations, or subsets that satisfy constraints. It explores a decision tree, pruning branches early when constraints are violated.
You'll see this in constraint satisfaction, puzzle solving, and exhaustive enumeration problems. If you can explain these concepts in your own words, you'll solve related problems faster under interview pressure.
