2316. Count Unreachable Pairs of Nodes in an Undirected Graph

class Solution {
public:
    long long dfs(int start, vector<bool> &visited, vector<int> adj[]){
        visited[start] = 1;
        int res = 1;
        for(auto i : adj[start]){
            if(!visited[i]){
                res += dfs(i, visited, adj);
            }
        }
        return res;
    }
public:
    long long countPairs(int n, vector<vector<int>>& edges) {
        vector<int> graph[n];
        vector<int>compare;
        vector<bool>visited(n,false);
        for(auto e : edges){
            graph[e[0]].push_back(e[1]);
            graph[e[1]].push_back(e[0]);
        }
        for(int i = 0; i < n; i++){
            if(!visited[i]){
                long long result = dfs(i, visited,graph);
                compare.push_back(result);
            }
        }
        int size = compare.size();
        vector<int> suffixvar(size , 0);
        suffixvar[size-1] = 0;
        for(int i = size-2; i >= 0; i--){
            suffixvar[i] = suffixvar[i+1] + compare[i+1];
        }
        long long resultnew = 0;
        for(int i = 0; i < size; i++){
            resultnew  += (compare[i]*1LL*suffixvar[i]);
        }
        return resultnew;
    }
};