Leetcode 40. 组合总和 II

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

代码如下:

public static List<List<Integer>> combinationSum2(int[] candidates, int target) {
        Set<String> set = new HashSet<>();
        //先排序
        Arrays.sort(candidates);
        List<List<Integer>> result = new ArrayList<>();
        for (int i = 0; i < candidates.length; i++) {
            if (candidates[i] > target) {
                continue;
            }
            List<List<Integer>> combination = combination(candidates, i, target);
            if (!combination.isEmpty()) {
                for (List<Integer> list : combination) {
                    if (set.add(Arrays.toString(list.toArray()))) {
                        result.add(list);
                    }
                }
            }
        }
        return result;
    }
    
//以索引位置i处的元素结尾，且组合出来的结果=target
    public static List<List<Integer>> combination(int[] candidates, int i, int target) {
        List<List<Integer>> result = new ArrayList<>();
        if (target == 0) {
            result.add(Arrays.asList());
            return result;
        }
        if (target == candidates[i]) {
            result.add(Arrays.asList(target));
            return result;
        }
        if (target - candidates[i] < 0) {  //
            return result;
        }
        int lastIndex = i - 1;
        if (lastIndex == 0 && candidates[0] == target - candidates[i]) {
            result.add(Arrays.asList(candidates[0], candidates[1]));
            return result;
        }
        int repeatCount = 1;
        while (lastIndex > 0 && candidates[lastIndex] == candidates[i]) {
            lastIndex--;
            repeatCount++;
        }
        for (int m = 1; m <= repeatCount; m++) {
            int n = lastIndex;
            while (n >= 0) {
                List<List<Integer>> combination = combination(candidates, n, target - m * candidates[i]);
                for (List<Integer> list : combination) {
                    List<Integer> integers = new ArrayList<>(list);
                    for (int j = 0; j < m; j++) {
                        integers.add(candidates[i]);
                    }
                    result.add(integers);
                }
                n--;
            }
        }
        return result;
    }