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

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

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

答案

class Solution {
    public List<List<Integer>> combinationSum(int[] candidates, int target) {
        List<List<Integer>> list = new ArrayList<List<Integer>>();
        List<Integer> curr = new ArrayList<>();
        Arrays.sort(candidates);
        recur(candidates, target, 0, list, curr, 0);
        return list;
    }
    
    private void recur(int[] candidates, int target, int curr_sum, List<List<Integer>> list, List<Integer> curr, int start) {
        if(curr_sum == target) {
            list.add(new ArrayList<>(curr));
            return;
        }
        if(curr_sum > target) return;
        
        for(int i = start; i < candidates.length; i++) {
            curr.add(candidates[i]);
            recur(candidates, target, curr_sum + candidates[i], list, curr, i);
            curr.remove(curr.size() - 1);
            
        }
    }
}