Find_Players_With_Zero_Or_One_Losses.cpp

PROBLEM STATEMENT :-
  You are given an integer array matches where matches[i] = [winneri, loseri] indicates that the player winneri defeated player loseri in a match.
  Return a list answer of size 2 where:
answer[0] is a list of all players that have not lost any matches.
answer[1] is a list of all players that have lost exactly one match.
The values in the two lists should be returned in increasing order.

Note: You should only consider the players that have played at least one match. The testcases will be generated such that no two matches will have the same outcome.
 
Example 1:
Input: matches = [[1,3],[2,3],[3,6],[5,6],[5,7],[4,5],[4,8],[4,9],[10,4],[10,9]]
Output: [[1,2,10],[4,5,7,8]]
Explanation:
Players 1, 2, and 10 have not lost any matches.
Players 4, 5, 7, and 8 each have lost one match.
Players 3, 6, and 9 each have lost two matches.
Thus, answer[0] = [1,2,10] and answer[1] = [4,5,7,8].
  
Example 2:
Input: matches = [[2,3],[1,3],[5,4],[6,4]]
Output: [[1,2,5,6],[]]
Explanation:
Players 1, 2, 5, and 6 have not lost any matches.
Players 3 and 4 each have lost two matches.
Thus, answer[0] = [1,2,5,6] and answer[1] = [].
  
  SOLUTION :-
    class Solution {
public:
    vector<vector<int>> findWinners(vector<vector<int>>& matches) 
    {
        vector<vector<int>> ans;
        vector<int> w,l;
        map<int,int> hash1, hash2, mp1;
        for(int i=0; i<matches.size(); i++)
        {
            int win = matches[i][0], loss = matches[i][1];
            hash1[win]++;
            hash2[loss]++;
            mp1[win]++;
            mp1[loss]++;
        }
        for(auto it=hash2.begin(); it!=hash2.end(); it++)
        {
            if(it->second==1)
                l.push_back(it->first);
        }
        for(auto it = mp1.begin(); it!=mp1.end(); it++)
        {
            if(hash1.find(it->first)!=hash1.end() && hash1[it->first])
            {
                if(it->second == hash1[it->first])
                    w.push_back(it->first);
            }
        }
        sort(w.begin(), w.end());
        sort(l.begin(), l.end());
        ans.push_back(w);
        ans.push_back(l);
        return ans;
    }
};