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N-Queens separates candidates who know backtracking from those who understand constraint propagation. The O(1) diagonal check using sets is what interviewers want to see.
AdminAugust 2, 20264 min read
The duplicate-skip pattern is what separates Combination Sum I from II. Master sort + skip, in-place grid marking for Word Search, and why `i > start` matters.
AdminAugust 2, 20265 min read
Backtracking is just DFS with an undo step. Master the three templates for subsets, permutations, and combinations — and the one mistake that ruins every solution.
AdminAugust 2, 20265 min read