topcode SRM 577 DIV2 EllysRoomAssignmentsDiv2

很郁闷的一题，一定要认真读题目，特别注意这句话   Concatenate its elements to obtain one long string，，，一定要理解这句话

#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <sstream>
#include <numeric>
using namespace std;

class EllysRoomAssignmentsDiv2{
public:
    double getProbability(vector <string> ratings){
        string split="";
        string all = accumulate(ratings.begin(),ratings.end(),split);
        stringstream sst(all);
        vector<int> score;
        int tmp;
        while(sst >> tmp) score.push_back(tmp);
        int score_elly = score[0];
        sort(score.begin(),score.end(),greater<int>());
        int cnt_elly = 0;
        for(int i = 0 ; i < score.size(); i ++  ){
            if( score[i] == score_elly) {
                cnt_elly = i;break;
            }
        }
        int R = score.size()%20 ? score.size()/20+1 : score.size()/20;
        if(R <= 1 || cnt_elly == 0 ) return 1.0;
        else if( cnt_elly < R ) return 0.0;
        else return 1.0/R;

    }
};