首页 > itarticle > [leetcode] problem 39 – combination sum

[leetcode] problem 39 – combination sum

admin 11月 13, 2020 0

Given a set of candidate numbers (candidates) (without duplicates) and a target number (target), find all unique combinations in candidates where the candidate numbers sums to target.

The same repeated number may be chosen from candidates unlimited number of times.

Note

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

Example

No.1

Input: candidates = [2,3,6,7], target = 7,
A solution set is:

[
  [7],
  [2,2,3]
]

No.2

Input: candidates = [2,3,5], target = 8,
A solution set is:

[
  [2,2,2,2],
  [2,3,3],
  [3,5]
]

Code

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

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

    return result;
}

private void (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++) {
        combination.add(candidates[i]);
        combinationSumHelper(result, combination, candidates, target - candidates[i], i);
        combination.remove(combination.size() - 1);
    }
}