LeetCode 40. Combination Sum II

40. Combination Sum II

Difficulty:: Medium

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 1:

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

Example 2:

Input: candidates = [2,5,2,1,2], target = 5,
A solution set is:
[
  [1,2,2],
  [5]
]

Solution

Language: Java

class Solution {
    public List<List<Integer>> combinationSum2(int[] candidates, int target) {
        List<List<Integer>> result = new ArrayList<>();
        if (candidates == null || candidates.length == 0) {
            return result;
        }
        Arrays.sort(candidates);
        dfsHelper(candidates, 0, target, result, new ArrayList<>());
        return result;
    }
    
    private void dfsHelper(int[] candidates, int index, int target, 
                           List<List<Integer>> result, List<Integer> combination) {
        if (target == 0) {
            result.add(new ArrayList<>(combination));
            return;
        }
        for (int i = index; i < candidates.length; i++) {
            if (candidates[i] > target) {
                break;
            }
            if (i != index && candidates[i] == candidates[i - 1]) {
                continue;
            }
            combination.add(candidates[i]);
            dfsHelper(candidates, i + 1, target - candidates[i], result, combination);
            combination.remove(combination.size() - 1);
        }
    }
}