[LeetCode] Problem 40 - Combination Sum II

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

Each number in candidates may only be used once in the combination.

Note

  • All numbers (including target) will be positive integers.
  • The solution set must not contain duplicate combinations.

Example

No.1

Input: candidates = [10,1,2,7,6,1,5], target = 8,
A solution set is:

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

No.2

Input: candidates = [2,5,2,1,2], target = 5,

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5
A solution set is:
[
  [1,2,2],
  [5]
]

Code

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public List<List<Integer>> combinationSum2(int[] candidates, int target) {
    List<List<Integer>> result = new ArrayList<>();
    List<Integer> combination = new ArrayList<>();
    Arrays.sort(candidates);

    combinationSum2Helper(result, combination, candidates, target, 0);

    return result;
}

private void combinationSum2Helper(List<List<Integer>> result, List<Integer> combination, int[] candidates, int target, int idx) {
    if (target < 0)
        return;

    if (target == 0) {
        result.add(new ArrayList<>(combination));
        return;
    }

    for (int i = idx; i < candidates.length; i++) {
        if (i > idx && candidates[i] == candidates[i - 1])
            continue;

        combination.add(candidates[i]);
        combinationSum2Helper(result, combination, candidates, target - candidates[i], i + 1);
        combination.remove(combination.size() - 1);
    }
}