poj2112 Electricity(割点应用)

const int maxn = 10010;
// vector<vector<int> > G;
int head[maxn], pnt[maxn<<2], nxt[maxn<<2], ecnt;
int dfn[maxn], low[maxn], depth;
int belong[maxn], block;
int in[maxn];
int cnt[maxn];
int n, m;
int ans;
void dfs(int u,int root) {
dfn[u] = low[u] = ++depth;
in[u] = 1;
// st.push(u);
int child = 0;
// int Size = G[u].size();
for (int i = head[u];~i;i = nxt[i]) {
int v = pnt[i];
if (dfn[v] == -1) {
child++;
dfs(v, root);
low[u] = min(low[u], low[v]);
if (low[v] >= dfn[u] && u != root) cnt[u]++;
}else if (in[v])low[u] = min(low[u], dfn[v]);
}

if (u == root && child >= 2) cnt[u] = child - 1;
ans = max(ans, cnt[u]);
}
void addedge(int u,int v) {
pnt[ecnt] = v, nxt[ecnt] = head[u], head[u] = ecnt++;
}
int main(int argc, const char * argv[])
{
// freopen("in.txt","r",stdin);
// freopen("out.txt","w",stdout);
// clock_t _ = clock();

while(scanf("%d%d", &n, &m) != EOF) {
if (n == 0 && m == 0) break;
// G.clear();G.resize(n + 2);
memset(head, -1,sizeof head), ecnt = 0;
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);
addedge(u, v);addedge(v, u);
}
if (m == 0) {printf("%d\n", n - 1);continue;}
memset(dfn, -1,sizeof dfn), depth = block = 0;
memset(cnt, 0, sizeof cnt);
ans = 0;
for (int i = 0;i < n;++i)
if (dfn[i] == -1) dfs(i, i), block++;
// int ans = 0;
// for (int i = 0;i < n;++i)
//     ans = max(ans, block + cnt[i]);
// cout << ans << endl;
printf("%d\n", ans + block);
}

// printf("\nTime cost: %.2fs\n", 1.0 * (clock() - _) / CLOCKS_PER_SEC);
return 0;
}