Combination Sum
Given an array of distinct integers and a target Return all unique combinations that sum to the target Each number can be used unlimited times Example: candidates = [2,3,6,7], target = 7 => [[2,2,3],[7]]
This one has lots of possibilities, and it's really testing whether you can explore them systematically. Interviewers love it because it reveals your structured exploration and your edge-case discipline. If you can explain your pruning, this stops feeling like brute force.
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