Leetcode-5087 Letter Tile Possibilities(活字印刷)

#define _for(i,a,b) for(int i = (a);i < b;i ++)

class Solution
{
    public:
        set<string> s;
        int numTilePossibilities(string tiles)
        {
            s.clear();
            int rnt = 0;
            for (int S = 1; S < 1 << tiles.size(); S ++)
            {
                string tmp;
                _for(i,0,tiles.size())
                {
                    if(S>>i & 0x1)
                        tmp += tiles[i];
                }
                sort(tmp.begin(),tmp.end());
                do
                {
                    if(!s.count(tmp))
                    {
                        rnt ++;
                        s.insert(tmp);
                    }
                }while(next_permutation(tmp.begin(),tmp.end()));
            }
            return rnt;
        }
};