LeetCode 39. Combination Sum

https://leetcode-cn.com/problems/combination-sum/solution/hui-su-suan-fa-jian-zhi-python-dai-ma-java-dai-m-2/

https://leetcode-cn.com/problems/combination-sum/solution/hui-su-suan-fa-tao-mo-ban-ji-ke-by-jeromememory/

class Solution {
    public List> combinationSum(int[] candidates, int target) {
        List> res = new ArrayList<>();
        Arrays.sort(candidates);
        backtrack(candidates, target, 0, new ArrayList<>(), res);
        return res;
    }
    private void backtrack(int[] candidates, int remain, int start, List path, List> res){
        if(remain == 0){
            res.add(new ArrayList<>(path));
            return;
        }
        for(int i = start; i < candidates.length; i++){
            if(candidates[i] > remain){
                break;
            }
            path.add(candidates[i]);
            backtrack(candidates, remain - candidates[i], i, path, res);
            path.remove(path.size() - 1);
        }
    }
}