Day 16 — Backtracking

What you’ll learn here

• The choose → recurse → un-choose template that defines backtracking
• Pruning — the difference between brute force and “smart brute force”
• Heavyweight problems: N-Queens, Sudoku Solver, Word Search, Combination Sum, Letter Combinations
• Bitmask state-space search for problems with up to 20 elements

Recursion’s Subsets and Permutations were the warm-up. This chapter is where backtracking really earns its keep.