LeetCode 90. 子集 II（回溯+剪枝）

示例:

输入: [1,2,2]
输出:
[
  [2],
  [1],
  [1,2,2],
  [2,2],
  [1,2],
  []
]

class Solution {
public:
    vector<vector<int>> subsetsWithDup(vector<int>& nums) {
        vector<int> sub;
        vector<vector<int>> ans;
        ans.push_back({});
        sort(nums.begin(), nums.end());
        int i, j, left = 0, right;
        for(i = 0; i < nums.size(); ++i)
        {
            if(i != 0 && (nums[i-1] != nums[i]))
                left = 0;
            right = ans.size();
            for(j = left; j < right; ++j)
            {
                sub = ans[j];
                sub.push_back(nums[i]);
                ans.push_back(sub);
            }
            left = ans.size()-(right-left);
        }
        return ans;
    }
};

class Solution {
public:
    vector<vector<int>> subsetsWithDup(vector<int>& nums) {
        sort(nums.begin(), nums.end());
        vector<int> sub;
        vector<vector<int>> ans;
        ans.push_back({});
        bt(nums,sub,ans,0);
       	return ans;
    }
    void bt(vector<int>& nums,vector<int> sub, vector<vector<int>> &ans, int i)
    {
    	for(int idx = i; idx < nums.size(); ++idx)
        {
            if(idx > i && nums[idx] == nums[idx-1])
                continue;
            sub.push_back(nums[idx]);
            ans.push_back(sub);
            bt(nums,sub,ans,idx+1);
            sub.pop_back();
        }
    }
};