LeetCode: Count Nodes With the Highest Score

class Solution {
public:

    vector <int> g[100010];
    int node[100010];

    int dfs(int u, int p){
        node[u] = 1;
        for(auto v: g[u]){
            if(v != p){
                node[u] += dfs(v, u);
            }
        }
        return node[u];
    }

    int countHighestScoreNodes(vector<int>& parents){
        int n = parents.size();
        for(int u=1;u<=n-1;u++){
            int v = parents[u];
            g[parents[u]].push_back(u);
        }

        dfs(0, -1);

        long long mx = 0;
        int cnt = 0;
        for(int u=0;u<=n-1;u++){
            long long cost = max(1, n - node[u]);
            for(auto v: g[u])
                cost = (long long)((long long) cost * (long long) node[v]);
            if(cost > mx) mx = cost, cnt = 1;
            else if(cost == mx) cnt ++;
        }

        return cnt;
    }
};