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题目传送地址: ​​https://leetcode.cn/problems/combination-sum/submissions/​​

代码如下

//递归解法
  public static List<List<Integer>> combinationSum(int[] candidates, int target) {
        //排序
        Arrays.sort(candidates);
        List<List<Integer>> result = new ArrayList<>();
        for (int i = 0; i < candidates.length; i++) {
            List<List<Integer>> combination = combination(candidates, i, target);
            if (!combination.isEmpty()) {
                result.addAll(combination);
            }
        }
        return result;
    }

    //算出以位置i的元素结尾，且符合最终结果的list
    public static List<List<Integer>> combination(int[] candidates, int i, int target) {
        List<List<Integer>> result = new ArrayList<>();
        if (i == 0) {
            if (target % candidates[0] == 0) {
                List<Integer> list = new ArrayList<>();
                while (target > 0) {
                    list.add(candidates[0]);
                    target = target - candidates[0];
                }
                result.add(list);
                return result;
            } else {
                return result;
            }
        }
        if (candidates[i] == target) {
            result.add(Arrays.asList(target));
            return result;
        }
        int[] range = Arrays.copyOfRange(candidates, 0, i);
        int count = 0;
        while (target >= candidates[i]) {
            int lastIndex = i - 1;
            count++;
            while (lastIndex >= 0) {
                List<List<Integer>> lists = combination(range, lastIndex, target - candidates[i]);
                if (!lists.isEmpty()) {
                    for (List<Integer> list : lists) {
                        List<Integer> integers = new ArrayList<>(list);
                        for (int m = 0; m < count; m++) {
                            integers.add(candidates[i]);
                        }
                        result.add(integers);
                    }
                }
                lastIndex--;
            }
            target = target - candidates[i];
        }
        return result;
    }