40. Combination Sum II.java

class Solution {
    public List<List<Integer>> combinationSum2(int[] candidates, int target) {
        List<List<Integer>> list = new ArrayList<>();
        Arrays.sort(nums);
        backtrack(list, new ArrayList<>(), nums, target, 0);
        return list;
    
}

    private void backtrack(List<List<Integer>> list, List<Integer> tempList, int [] nums, int remain, int start){
        if(remain < 0) 
            return;
        else if (remain == 0) 
            list.add(new ArrayList<>(tempList));
        else{
            for (int i = start; i < nums.length; i++){
                if (i > start && nums[i] == nums[i - 1]) continue; // skip duplicates
                tempList.add(nums[i]);
                backtrack(list, tempList, nums, remain - nums[i], i + 1);
                tempList.remove(tempList.size() - 1); 
            }
        }
    } 
}