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Reverse Nodes in k-Group
This one has lots of possibilities, and it's really testing whether you can explore them systematically. It's a hard one for a reason: it stresses structured exploration when the rules pile up. The gotcha is duplicates and dead ends—good pruning and ordering rules make this manageable.
Learn this pattern
Backtracking Pattern
Backtracking explores a decision tree with DFS, choosing an option, recursing, then undoing the choice. Use it for permutations, combinations, subsets, and constraint-satisfaction problems like N-Queens.
Meet your coaches
Talk through the problem while you code. Signed-in reps become prep memory for the next session.
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Backtracking Pattern gives you a useful next rep while you are still on your phone.