hdu4635Strongly connected

http://acm.hdu.edu.cn/showproblem.php?pid=4635

tarjan缩点 统计缩点后每个结点的出度入度 将那个包含原来点数最少的 且出度或者入度为0的大节点看作一个整体内部连边n*（n-1)个 连全部的； 其它的点为一整体连全部的 再两者连一同向的边 保证它的出度或者入度依旧为0的情况下任意连 最后减去原来的边M

 

  1 #include <iostream>

  2 #include<cstring>

  3 #include<cstdio>

  4 #include<stdlib.h>

  5 #include<stack>

  6 using namespace std;

  7 #define N 100010

  8 #define M 100010

  9 #define INF 0xfffffff

 10 int a[110][110];

 11 stack<int>s;

 12 struct node

 13 {

 14     int u,v,next;

 15 }ed[M*2];

 16 int scc,sccno[N],head[N],lowlink[N],pre[N],dep,num[N],x[M],y[M],din[N],dout[N],o;

 17 void init()

 18 {

 19     o = 0;

 20     memset(head,-1,sizeof(head));

 21 }

 22 void add(int u,int v)

 23 {

 24     ed[o].u = u;

 25     ed[o].v = v;

 26     ed[o].next = head[u];

 27     head[u] = o++;

 28 }

 29 void dfs(int u)

 30 {

 31     int i;

 32     lowlink[u] = pre[u] = ++dep;

 33     s.push(u);

 34     for( i = head[u] ; i != -1 ; i = ed[i].next)

 35     {

 36         int v = ed[i].v;

 37         if(!pre[v])

 38         {

 39             dfs(v);

 40             lowlink[u] = min(lowlink[u],lowlink[v]);

 41         }

 42         else if(!sccno[v])

 43         lowlink[u] = min(lowlink[u],pre[v]);

 44     }

 45     if(lowlink[u]==pre[u])

 46     {

 47         scc++;

 48         for(;;)

 49         {

 50             int x = s.top();

 51             s.pop();

 52             sccno[x] = scc;

 53             if(x==u) break;

 54         }

 55     }

 56 }

 57 void find_scc(int n)

 58 {

 59     for(int i = 1; i <= n ;i++)

 60     if(!pre[i])

 61     dfs(i);

 62 }

 63 int main()

 64 {

 65     int i,t,n,m,a,b,kk=0;

 66     cin>>t;

 67     while(t--)

 68     {

 69         init();kk++;

 70         memset(num,0,sizeof(num));

 71         memset(pre,0,sizeof(pre));

 72         memset(din,0,sizeof(din));

 73         memset(dout,0,sizeof(dout));

 74         memset(sccno,0,sizeof(sccno));

 75         scanf("%d%d",&n,&m);

 76         for(i = 1; i <= m ; i++)

 77         {

 78             scanf("%d%d",&a,&b);

 79             x[i] = a;y[i] = b;

 80             add(a,b);

 81         }

 82         scc=0;dep=0;

 83         find_scc(n);

 84         printf("Case %d: ",kk);

 85         if(scc==1)

 86         {

 87             cout<<"-1\n";

 88             continue;

 89         }

 90         for(i = 1; i <= n ; i++)

 91         num[sccno[i]]++;

 92         for(i = 1; i <= m ;i++)

 93         {

 94             if(sccno[x[i]]!=sccno[y[i]])

 95             {

 96                 dout[sccno[x[i]]]++;

 97                 din[sccno[y[i]]]++;

 98             }

 99         }

100         long long minz = INF;

101         for(i = 1 ;i <= scc ; i++)

102         if(minz>num[i]&&(din[i]==0||dout[i]==0))

103         minz = num[i];

104         long long ss=0;

105         ss = minz*(minz-1)+(n-minz)*(n-minz-1)+minz*(n-minz);

106         cout<<ss-m<<endl;

107     }

108     return 0;

109 }

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