3238. Find the Number of Winning Players

You are given an integer n representing the number of players in a game and a 2D array pick where pick[i] = [xi, yi] represents that the player xi picked a ball of color yi.

Player i wins the game if they pick strictly more than i balls of the same color. In other words,

• Player 0 wins if they pick any ball.
• Player 1 wins if they pick at least two balls of the same color.
• …
• Player i wins if they pick at leasti + 1 balls of the same color.

Return the number of players who win the game.

Note that multiple players can win the game.

class Solution {
public:
    int winningPlayerCount(int n, vector<vector<int>>& pick) {
        unordered_map<int, unordered_map<int,int>> freq;
        unordered_set<int> us;
        for(auto& vec : pick) {
            int x = vec[0], y = vec[1];
            if(++freq[x][y] > x) us.insert(x);
        }
        return us.size();
    }
};