Combination Sum II

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Problem

Given a collection of candidate numbers that may contain duplicates, and a target, find all unique combinations where the chosen numbers sum to the target; each number may be used at most once per combination.

Examples

Example 1

Input:candidates = [10,1,2,7,6,1,5], target = 8

Output:[[1,1,6],[1,2,5],[1,7],[2,6]]

Constraints

1 <= candidates.length <= 100

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How to approach it: the Backtracking pattern

Explore a decision one choice at a time, undo it if it doesn't lead anywhere, and try the next option. It's a systematic way to generate every valid combination, permutation, or arrangement.

Look for this pattern when

The problem asks for "all possible" combinations, subsets, permutations, or valid arrangements.
A greedy or direct-formula approach doesn't work because you genuinely need to explore multiple branches.

Read the full Backtracking guide →

Video walkthroughs

Original problem on LeetCode ↗