【POJ】2117 Electricity

无向图求割点和连通块。

 /* POJ2117 */
 #include <iostream>
 #include <vector>
 #include <algorithm>
 #include <cstdio>
 #include <cstring>
 #include <cstdlib>
 using namespace std;

 #define MAXN 10005

 vector<int> vc[MAXN];
 int low[MAXN], pre[MAXN];
 int n, m;
 int dfs_clock, ans, link;

 void init() {
     int i;

     for (i=; i<n; ++i)
         vc[i].clear();

     memset(pre, , sizeof(int)*n);
     dfs_clock = ans = link = ;
 }

 void tarjan(int u, int fa) {
     int i, j, k, v;
     int child = ;
     int cnt = ;

     pre[u] = low[u] = ++dfs_clock;
     for (i=; i<vc[u].size(); ++i) {
         v = vc[u][i];
         if (!pre[v]) {
             ++child;
             tarjan(v, u);
             low[u] = min(low[u], low[v]);
             if (low[v] >= pre[u]) {
                 ++cnt;
             }
         } else if (pre[v]<pre[u] && v!=fa){
             low[u] = min(low[u], pre[v]);
         }
     }
     if (fa == -) {
         if (child > )
             ans = max(ans, child-);
     } else {
         ans = max(ans, cnt);
     }
 }

 int main() {
     int i, j, k;

     #ifndef ONLINE_JUDGE
         freopen("data.in", "r", stdin);
         freopen("data.out", "w", stdout);
     #endif

     while (scanf("%d %d",&n,&m)!=EOF && (n||m)) {
         if (m == ) {
             printf("%d\n", n-);
             continue;
         }
         init();
         for (i=; i<m; ++i) {
             scanf("%d %d", &j, &k);
             vc[j].push_back(k);
             vc[k].push_back(j);
         }
         for (i=; i<n; ++i) {
             if (!pre[i]) {
                 ++link;
                 tarjan(i, -);
             }
         }
         printf("%d\n", ans+link);
     }

     return ;
 }