Just focus on the bold font, rest is input output.
#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
#include <queue>
using namespace std;
int main() {
/* Enter your code here. Read input from STDIN. Print output to STDOUT */
int q;
cin >> q;
while (q--) {
int n, m, rdcs, libcs;
cin >> n >> m >> libcs >> rdcs;
vector<long long> arr[n+1];
vector<bool> visited(n+1,false);
int x, y;
for (int i = 0; i < m; i++) {
cin >> x >> y;
arr[x].push_back(y);
arr[y].push_back(x);
}
long long cst = 0;
/*
for (int i = 0; i < n; i++) {
if (!visited[i+1]) {
int j;
for (j = 0; j < arr[i+1].size(); j++) {
if (visited[arr[i+1][j]]) {
break;
}
}
if (j == arr[i+1].size()) {
cst += min((long long)(arr[i+1].size() * rdcs + libcs), (long long)(libcs * (arr[i+1].size() + 1)));
for (j = 0; j < arr[i+1].size(); j++) {
visited[arr[i+1][j]] = true;
}
}
else {
cst += min(libcs, rdcs);
}
visited[i+1] = true;
}
} */
///// bfs ///
for (int i = 1; i <= n; i++) {
if (!visited[i]) {
queue<int> q;
visited[i] = true;
int cnt = 0;
q.push(i);
while (!q.empty()) {
int v = q.front();
q.pop();
cnt++;
for (int j = 0; j < arr[v].size(); j++) {
if (visited[arr[v][j]]) continue;
visited[arr[v][j]] = true;
q.push(arr[v][j]);
}
}
cst += min((cnt - 1) * rdcs + libcs, cnt * libcs);
}
}
cout << cst << endl;
}
return 0;
}