39. 组合总和

39. 组合总和

回溯

class Solution {
    List<List<Integer>> res = new ArrayList<>();
    List<Integer> path = new ArrayList<>();

    public List<List<Integer>> combinationSum(int[] candidates, int target) {
        backtrack(candidates, target, 0);
        return res;
    }

    void backtrack(int[] candidates, int target, int ind){
        if(target < 0) return;
        if(target == 0){
            res.add(new ArrayList<>(path));
            return;
        }

        for(int i = ind; i < candidates.length; i++){
            path.add(candidates[i]);
            target -= candidates[i];
            backtrack(candidates, target, i);
            target += candidates[i];
            path.remove(path.size() - 1);
        }
    }
}