题解

#include <iostream>
#include <vector>
using namespace std;

int main() {
    int n, m;
    cin >> n >> m;
    vector<vector<int>> adj(n + 1); // 邻接表，结点编号从1到n

    for (int i = 0; i < m; ++i) {
        int u, v;
        cin >> u >> v;
        adj[u].push_back(v);
        adj[v].push_back(u);
    }

    long long ans = 0;
    for (int u = 1; u <= n; ++u) {
        long long d = adj[u].size();
        ans += d * (d - 1) / 2;
    }

    cout << ans << endl;
    return 0;
}