<ul><li>Given a collection of candidate numbers and a key, find all unique combinations in candidates where the candidate numbers sum to target.</li><li>The solution set must not contain duplicate combinations.</li><li>Two possible solutions for this problem are backtracking and DFS.</li><li>The DFS solution involves going deep into the tree and adding elements to the combination set.</li></ul>

Given a collection of candidate numbers and a key, find all unique combinations in candidates where the candidate numbers sums to target.

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