poj1523(割点)

1.思路参考刘汝佳的算法艺术与信息学竞赛。

2.代码。

#include<cstdio>#include<iostream>using namespace std;//   freopen("data.in","r",stdin);#include<cstring>#define N 1005bool G[N][N];int _V;int root;bool vis[N];int deep[N],ancestor[N];bool cutP[N];//int son[N];int cutE[N][N];void init(){    memset(G,0,sizeof(G));    memset(cutP,0,sizeof(cutP));  //  memset(son,0,sizeof(son));    memset(deep,-1,sizeof(deep));    memset(vis,0,sizeof(vis));    _V=2;    root=1;}void dfs(int u,int father,int d){    deep[u]=ancestor[u]=d;    int son=0;    for(int v=1; v<=_V; v++)    {        if(G[u][v])        {            if(deep[v]==-1)            {                son++;                dfs(v,u,d+1);                ancestor[u]=ancestor[u]>ancestor[v]?ancestor[v]:ancestor[u];            }            else if(v!=father)            {                ancestor[u]=ancestor[u]>deep[v]?deep[v]:ancestor[u];            }        }    }    if(u==root)    {        if(son>1)cutP[root]=true;        else cutP[root]=false;    }    else if(ancestor[u]>=deep[father])//    {        cutP[father]=true;        cutE[father][u]=true;    }}void output(int Case){    printf("Network #%d\n",Case);    bool exist=false;    for(int u=1; u<=_V; u++)    {        if(cutP[u])        {            exist=true;            int branch;            if(u==1)branch=0;            else branch=1;            bool f=false;            for(int v=1;v<=_V;v++)            {                if(G[u][v])                {                    if(ancestor[v]>deep[u])branch++;                    if(ancestor[v]==deep[u])f=true;                }            }            printf("  SPF node %d leaves %d subnets\n",u,branch+f);        }    }    if(!exist)printf("  No SPF nodes\n");    cout<<endl;}int main(){ //   freopen("data.in","r",stdin);    int Case=1;    int u,v;    while(~scanf("%d",&u)&&u)    {        init();        scanf("%d",&v);        vis[u]=vis[v]=G[u][v]=G[v][u]=true;        while(~scanf("%d",&u)&&u)        {            scanf("%d",&v);            G[u][v]=G[v][u]=true;            if(!vis[u])            {                vis[u]=true;                _V++;            }            if(!vis[v])            {                vis[v]=true;                _V++;            }        }        dfs(1,0,0);        output(Case);        Case++;    }    return 0;}