POJ1523 SPF （求割点）

#include<cstdio>
#include<cstring>
#define min(a,b) (a)<(b)?(a):(b)
#define MAXN 5005
#define MAXM 20005
struct node
{
int v;
node *next;
} Edge[MAXM], *Adj[MAXN], *Mcnt = Edge;
void addedge(int u, int v)
{
node *t = ++Mcnt;
t->v = v;
t->next = Adj[u];
Adj[u] = t;
}
int dfn[MAXN], low[MAXN], cnt, rtson;
int isc[MAXN]; // 表示去掉某个点能将图分成几部分
void dfs(int u, int fa)
{
dfn[u] = low[u] = ++cnt;
int son = 0;
for(node *p = Adj[u]; p; p = p->next)
{
if(!dfn[p->v])
{
dfs(p->v, u);
low[u] = min(low[u],low[p->v]);
if(low[p->v] >= dfn[u] && fa != -1) ++isc[u];
son++;
}
else if(p->v != fa)low[u] = min(low[u], dfn[p->v]);
}
if(fa == -1 && son > 1) rtson = son;
}
int main()
{
int t1, t2;
int Cas = 0;
while(~scanf("%d", &t1))
{
++Cas;
if(t1 == 0)return 0;
scanf("%d", &t2);
memset(Adj, 0, sizeof Adj);
memset(isc, 0, sizeof isc);
memset(dfn, 0, sizeof dfn);
memset(low, 0, sizeof low);
Mcnt = Edge;
cnt = 0;
rtson = 0;
addedge(t1, t2);
addedge(t2, t1);
while(~scanf("%d", &t1))
{
if(t1 == 0) break;
scanf("%d", &t2);
addedge(t1, t2);
addedge(t2, t1);
}
dfs(1, -1);
bool flag = 1;
printf("Network #%d\n",Cas);
if(rtson>1) isc[1] = rtson;
for(int i = 1; i <= cnt; i++)
if(isc[i])
{
printf("  SPF node %d leaves %d subnets\n", i, isc[i] + (i != 1)); //因为若不是根节点，除了能分出几个子树外，还留下了一块
flag = 0;
}
if(flag)
puts("  No SPF nodes");
putchar('\n');
}
return 0;
}