[LeetCode] Subsets II

题目描述:

Given a collection of integers that might contain duplicates, nums, return all possible subsets.

Note:

Elements in a subset must be in non-descending order.

The solution set must not contain duplicate subsets.

For example,
If nums =

[1,2,2]

, a solution is:

[
[2],
[1],
[1,2,2],
[2,2],
[1,2],
[]
]

解题思路：

回溯法

class Solution {
public:
vector<vector<int>> subsetsWithDup(vector<int>& nums) {
vector<vector<int>> result;
if (nums.size() == 0) {
return result;
}

sort(nums.begin(), nums.end());
vector<int> elem;

for (int i = 0; i <= nums.size(); ++i) {
subsets(nums, i, 0, result, elem);
}

return result;
}
private:
void subsets(const vector<int> &nums, int len, int cur, vector<vector<int>> &result, vector<int> &elem) {
if (elem.size() == len) {
result.push_back(elem);
return;
}

for (int i = cur; i < nums.size(); ++i) {
elem.push_back(nums[i]);
subsets(nums, len, i + 1, result, elem);
elem.pop_back();
// 跳过重复的元素
for (int j = i + 1; j < nums.size(); ++j) {
if (nums[j] != nums[i]) {
break;
}
++i;
}
}
}
};