N-Queens (LeetCode 51)N-Queens (LeetCode 51) in Java with recursive backtracking: place a queen row by row, check the column and both diagonals, then undo and try the next square.
Combination Sum (LeetCode 39)Combination Sum (LeetCode 39) in Java with recursive backtracking: reuse numbers freely, avoid duplicate combinations with a start index, then undo and try the next one.
Subsets (LeetCode 78)Subsets (LeetCode 78) in Java with recursive backtracking: generate every subset of an array using a start index, and how it differs from Combination Sum.
Word Search (LeetCode 79)Word Search (LeetCode 79) in Java with recursive backtracking on a grid: DFS letter by letter, and why un-marking visited cells is what makes it work.