[POJ 1523] SPF

这是一道求割点的入门题，没什么好讲的，给一组详细的样例数据以供参考：

输入：

1 2

5 4

3 1

3 2

3 4

3 5

0

 

1 2

2 3

3 4

4 5

5 1

0

 

1 2

2 3

3 4

4 6

6 3

2 5

5 1

0

 

1 2

0

 

1000 999

999 998

998 997

997 1000

0

 

1 2

2 3

0

 

1 2

1 3

1 4

1 5

0

 

1 2

1 3

1 4

2 3

2 5

2 6

3 7

3 8

7 8

0

 

1 2

1 3

1 4

1 5

2 3

2 4

2 5

3 4

3 5

4 5

0

 

0

输出：

Network #1
  SPF node 3 leaves 2 subnets


Network #2
  No SPF nodes


Network #3
  SPF node 2 leaves 2 subnets
  SPF node 3 leaves 2 subnets


Network #4
  No SPF nodes


Network #5
  No SPF nodes


Network #6
  SPF node 2 leaves 2 subnets


Network #7
  SPF node 1 leaves 4 subnets


Network #8
  SPF node 1 leaves 2 subnets
  SPF node 2 leaves 3 subnets
  SPF node 3 leaves 2 subnets


Network #9
  No SPF nodes

#include <iostream>#include <cstdio>#include <cstring>#include <stack>#include <algorithm>#include <vector>#define AddEdge(x,y) a.push_back(edge(x,y))#define MakeSmall(x,y) if(x>y) x=y#define MaxN 1010using namespace std;int head[MaxN],tot;int low[MaxN],dfn[MaxN],time;int SubNet[MaxN];int MinP;bool CutP[MaxN],v[MaxN];stack<int> st;struct edge{int v,next;edge(int x,int y):v(y),next(head[x]){head[x]=tot++;}};vector<edge> a;inline void InitGraph(){memset(head,-1,sizeof(head));memset(low,0,sizeof(low));memset(dfn,0,sizeof(dfn));memset(CutP,0,sizeof(CutP));memset(v,0,sizeof(v));memset(SubNet,0,sizeof(SubNet));while(!st.empty()) st.pop();time=tot=0,MinP=MaxN;a.clear();}inline bool init(){InitGraph();int x,y;scanf("%d",&x);if(!x) return 0;scanf("%d",&y);AddEdge(x,y),AddEdge(y,x);MakeSmall(MinP,x);MakeSmall(MinP,y);for(;;){cin>>x;if(!x) return 1;scanf("%d",&y);AddEdge(x,y);AddEdge(y,x);MakeSmall(MinP,x);MakeSmall(MinP,y);}}void tarjan(int x,int p){dfn[x]=low[x]=++time;int ChNum=0,y;st.push(x);v[x]=1;for(int i=head[x];~i;i=a[i].next){y=a[i].v;if(p==y) continue;if(!dfn[y]){ChNum++;tarjan(y,x);low[x]=min(low[x],low[y]);if(x!=p&&low[y]>=dfn[x]){CutP[x]=1;SubNet[x]++;}}else if(v[y])low[x]=min(low[x],dfn[y]);}if(dfn[x]==low[x]){do{y=st.top();st.pop();v[x]=0;}while(x!=y);}if(x==p&&ChNum>1){CutP[x]=1;SubNet[x]=ChNum-1;}}inline void work(int cas){printf("Network #%d\n",cas);tarjan(MinP,MinP);bool flag=0;for(int i=MinP;i<1001;i++)if(CutP[i])flag=1,printf("  SPF node %d leaves %d subnets\n",i,SubNet[i]+1);if(!flag) printf("  No SPF nodes\n");}int main(){int CASE=0;while(init()){work(++CASE);printf("\n");}return 0;}