Leetcode|子集|90.子集II（排序+first索引+跳过重复元素）

class Solution {
private:
    int size;
    vector<vector<int>> solution;
    vector<int> path;
public:
    void backtrack(vector<int>& nums, int first) {
        solution.emplace_back(path);
        // 2. 使用first索引
        for (int i = first; i < size; i++) {
        	// 3. 跳过重复元素
            if (i > first && nums[i] == nums[i-1]) continue;
            path.emplace_back(nums[i]);
            backtrack(nums, i + 1);
            path.pop_back();
        }
    }
    vector<vector<int>> subsetsWithDup(vector<int>& nums) {
        size = nums.size();
        // 1. 排序使重复元素相邻
        sort(nums.begin(), nums.end());
        backtrack(nums, 0);
        return solution;
    }
};