UVaLive/LA 6804 Group of Strangers（图论）

6804 - Group of Strangers

参考代码1：

// Author: Yuan Zhu#include <iostream>#include <cstdio>#include <vector>#include <cstring>#include <cmath>#include <algorithm>#include <set>#define ll long longusing namespace std;int t, n, m;vector<int> G[5010];pair<int, int> p[20010];int vis[5010][5010];int marked;void init() {    for(int i = 0; i < 5010; i++) G[i].clear();}void read() {    scanf("%d%d", &n, &m);    int u, v;    for (int i = 0; i < m; i++) {        scanf("%d%d", &u, &v);        G[u].push_back(v);        G[v].push_back(u);        p[i] = make_pair(u, v);    }}void solve(int ca) {    marked++;    ll S = n * 1LL * (n - 1) * 1LL * (n - 2) / 6;    ll one = 0, two = 0, three = 0;    int mm = 0;    int marked1;    int check[5010];    for (int i = 0; i < m; i++) {        int u = p[i].first, v = p[i].second;        if (vis[u][v] == marked) continue;        vis[u][v] = marked;        mm++;        marked1++;        for (int j = 0; j < G[u].size(); j++) check[G[u][j]] = marked1;        ll ct = 0;        for (int j = 0; j < G[v].size(); j++) {            if (check[G[v][j]] == marked1) ct++;        }        /*set<int> s;        for(int j=0;j<G[u].size();j++) s.insert(G[u][j]);        for(int j=0;j<G[v].size();j++) s.insert(G[v][j]);*/        one += ((ll)n - (ll)G[u].size() - (ll)G[v].size() + ct);        three += ct;        //cout<<u<<" "<<v<<" "<<n-(ll)s.size()<<endl;    }    two = (mm * 1LL * (n - 2) - one - three) / 2;    //cout<<one<<" "<<two<<" "<<three/3<<endl;    ll ans = S - one - two - three / 3;    printf("Case #%d: %lld\n", ca, ans);}int main() {    scanf("%d", &t);    for (int ca = 1; ca <= t; ca++) {        init();        read();        solve(ca);    }    return 0;}

参考代码2：

// Author: Yejie Zhou#include <iostream>#include <cstdio>#include <vector>#include <cstring>#define ll long longusing namespace std;int n, m;vector<int> g[5010];bool vis[5010][5010];int main () {    int T;    scanf("%d", &T);    int ncase = 1;    while (T--) {        scanf("%d%d", &n, &m);        for (int i = 1; i <= n; i++) {            g[i].clear();        }        memset(vis, 0, sizeof(vis));        for (int i = 0; i < m; i++) {            int u, v;            scanf("%d%d", &u, &v);            g[u].push_back(v);            g[v].push_back(u);            vis[u][v] = 1;            vis[v][u] = 1;        }        ll sum = 0;        int three = 0;        for (int i = 1; i <= n; i++) {            int num = g[i].size();            if (num >= 2)                sum += num * (num - 1) / 2;            for (int j = 0; j < num - 1; j++) {                for (int k = j + 1; k < num; k++) {                    if (vis[g[i][j]][g[i][k]])                        three++;                }            }        }        three /= 3;        ll ans = n * (n - 1) * (ll)(n - 2) / 6 - ((n - 2) * m - sum + three);        printf("Case #%d: %lld\n", ncase++, ans);    }    return 0;}