HDU 6165 FFF at Valentine(强连通 缩点 17多校第九场)

• 题目大意

  给定一个又向图，让你判断是否是对于给定的任意两个点都能从u到v或v到u

• 分析

  缩点成DAG之后，不断删掉度为0的点，如果某个时刻出现两个或以上入度为0的点则不满足
  算法的实现采用的是Tarjan算法求强连通分量缩点

• 代码

#include<cstdio>#include<iostream>#include<cmath>#include<cstring>#include<cstdlib>#include<queue>#include<map>#include<algorithm>#include<set>#include<stack>using namespace std;const int MAXN=1005;int T;int n,m;int DFN[MAXN];int LOW[MAXN];int vis[MAXN];int belong[MAXN];//belong[i]表示i属于缩点后的哪个节点int cnt;//缩点后的点数int tot;int in[MAXN];//保存缩点后每个点的入度int graph[MAXN][MAXN];struct Edge{      int v;      int next;}edge[MAXN*MAXN];int edgecount;int head[MAXN];void Init(){      edgecount=0;      memset(head,-1,sizeof(head));      memset(graph,0,sizeof(graph));}void Add_edge(int u,int v){      edge[++edgecount].v=v;      edge[edgecount].next=head[u];      head[u]=edgecount;}stack<int > St;void Tarjan(int u)//从节点x开始搜索{     DFN[u]=LOW[u]=++tot;     vis[u]=1;//为1表示在队列里面     St.push(u);     for(int k=head[u];k!=-1;k=edge[k].next)     {           int v=edge[k].v;           if(!DFN[v])//还未访问过           {                 Tarjan(v);                 LOW[u]=min(LOW[u],LOW[v]);           }           else if(vis[v])//被访问过，还在队列里           {                 LOW[u]=min(LOW[u],DFN[v]);           }     }     if(LOW[u]==DFN[u])     {           int x;           ++cnt;           while(1)           {                 x=St.top();                 St.pop();                 vis[x]=0;                 belong[x]=cnt;                 if(x==u)break;           }     }}bool Topo(){    int bj[MAXN];    memset(bj,0,sizeof(bj));    for(int k=1;k<=cnt;k++)    {        int sum=0;        int x;        for(int v=1;v<=cnt;v++)        {            if(in[v]==0 && bj[v]==0){sum++;x=v;}        }        if(sum>=2)return 0;        bj[x]=1;        for(int v=1;v<=cnt;v++)        {            if(graph[x][v]==1)in[v]--;        }    }    return 1;}void Solve(){    tot=0;    cnt=0;//缩点后的点数    memset(DFN,0,sizeof(DFN));    memset(LOW,0,sizeof(LOW));    memset(vis,0,sizeof(vis));    memset(in,0,sizeof(in));    while(!St.empty()) St.pop();    for(int i=1;i<=n;i++)    {          if(DFN[i]==0)Tarjan(i);    }    for(int u=1;u<=n;u++)    {          for(int k=head[u];k!=-1;k=edge[k].next)          {                int v=edge[k].v;                if(belong[u]!=belong[v])                {                      if(graph[belong[u]][belong[v]]==0)in[belong[v]]++;                      graph[belong[u]][belong[v]]=1;                }          }    }    //Test();    if(Topo())printf("I love you my love and our love save us!\n");    else printf("Light my fire!\n");}void In(){    int a,b;    scanf("%d%d",&n,&m);    for(int i=1;i<=m;i++)    {        scanf("%d%d",&a,&b);        Add_edge(a,b);    }}int main(){    //freopen("in.txt","r",stdin);    //freopen("out1.txt","w",stdout);    scanf("%d",&T);    while(T--)    {        Init();        In();        Solve();    }    return 0;}/*208 111 24 85 82 44 12 62 53 65 74 53 1*/