hdu--4912--终于解脱了

  1 #include <iostream>
  2 #include <cstring>
  3 #include <algorithm>
  4 using namespace std;
  5 
  6 int Ncnt , Qcnt;
  7 const int size = 100010;
  8 struct data
  9 {
 10     int id;
 11     int from;
 12     int to;
 13     int next;
 14     int lca;
 15 };
 16 data node[size*2];
 17 int Nhead[size];
 18 data query[size*2];
 19 data graph[size];
 20 int Qhead[size];
 21 bool vis[size];
 22 int father[size];
 23 int depth[size];
 24 bool check[size];
 25 
 26 bool cmp( data p , data q )
 27 {
 28     return depth[p.lca] > depth[q.lca];
 29 }
 30 
 31 void init( )
 32 {
 33     memset( Nhead , -1 , sizeof(Nhead) );
 34     memset( Qhead , -1 , sizeof(Qhead) );
 35     memset( vis , false , sizeof(vis) );
 36     memset( check , false , sizeof(check) );
 37     depth[1] = 0;
 38 }
 39 
 40 int find( int x )
 41 {
 42     return x == father[x] ? x : father[x] = find( father[x] );
 43 }
 44 
 45 void addNedge( int st , int end )
 46 {
 47     node[Ncnt].to = end;
 48     node[Ncnt].next = Nhead[st];
 49     Nhead[st] = Ncnt ++;
 50 }
 51 
 52 void addQedge( int id , int st , int end )
 53 {
 54     query[Qcnt].id = id;
 55     query[Qcnt].from = st;
 56     query[Qcnt].to = end;
 57     query[Qcnt].next = Qhead[st];
 58     Qhead[st] = Qcnt ++;
 59 }
 60 
 61 void lca_tarjan( int u )
 62 {
 63     int v;
 64     father[u] = u;
 65     vis[u] = true;
 66     for( int i = Nhead[u] ; ~i ; i = node[i].next )
 67     {
 68         v = node[i].to;
 69         if( !vis[v] )
 70         {
 71             depth[v] = depth[u] + 1;
 72             lca_tarjan( v );
 73             father[v] = u;
 74         }
 75     }
 76     for( int i = Qhead[u] ; ~i ; i = query[i].next )
 77     {
 78         v = query[i].to;
 79         if( vis[v] )
 80         {
 81             graph[ query[i].id ].lca = find(v);
 82         }
 83     }
 84 }    
 85 
 86 void dfs( int u )
 87 {
 88     int v;
 89     check[u] = true;
 90     for( int i = Nhead[u] ; ~i ; i = node[i].next )
 91     {
 92         v = node[i].to;
 93         if( !check[v] && depth[u]<depth[v] )
 94             dfs(v);
 95     }
 96 }
 97 
 98 int main()
 99 {
100     cin.sync_with_stdio(false);
101     int n , m , st , end , lca , ans , temp;
102     while( cin >> n >> m )
103     {
104         ans = Ncnt = Qcnt = 0;
105         init( );
106         for( int i = 0 ; i<n-1 ; i++ )
107         {
108             cin >> st >> end;
109             addNedge( st , end );
110             addNedge( end , st );
111         }
112         for( int i = 0 ; i<m ; i++ )
113         {
114             cin >> st >> end;
115             addQedge( i , st , end );
116             addQedge( i , end , st );
117             graph[i].from = st;
118             graph[i].to = end;
119         }
120         lca_tarjan(1);
121         sort( graph , graph+m , cmp );
122         for( int i = 0 ; i<m ; i++ )
123         {
124             st = graph[i].from;
125             end = graph[i].to;
126             lca = graph[i].lca;
127             if( !check[st] && !check[end] )
128             {
129                 ans ++;
130                 dfs( lca );
131             }
132         }
133         cout << ans << endl;
134     }
135     return 0;
136 }