hdu--2586--lca_tarjan<证明tarjan这个人很流弊>

  1 #include <iostream>
  2 #include <cstring>
  3 using namespace std;
  4 
  5 int cnt1 , cnt2;
  6 const int size1 = 40010;
  7 const int size2 = 210;
  8 struct graph
  9 {
 10     int from;
 11     int to;
 12     int val;
 13     int next;
 14     int lca;
 15 };
 16 graph edge[size1*2];
 17 int Ehead[size1];
 18 graph node[size2*2];
 19 int Nhead[size1];
 20 bool vis[size1];
 21 int dist[size1];
 22 int father[size1];
 23 
 24 void init( )
 25 {
 26     memset( Ehead , -1 , sizeof(Ehead) );
 27     memset( Nhead , -1 , sizeof(Nhead) );
 28     memset( dist , 0 , sizeof(dist) );
 29     memset( vis , false , sizeof(vis) );
 30 }
 31 
 32 int find( int x )
 33 {
 34     return x == father[x] ? x : father[x] = find( father[x] );
 35 }
 36 
 37 
 38 void addEdge( int from , int to , int val )
 39 {
 40     edge[cnt1].to = to;
 41     edge[cnt1].val = val;
 42     edge[cnt1].next = Ehead[from];
 43     Ehead[from] = cnt1 ++;
 44 }
 45 
 46 void addQueryEdge( int from , int to )
 47 {
 48     node[cnt2].from = from;
 49     node[cnt2].to = to;
 50     node[cnt2].next = Nhead[from];
 51     Nhead[from] = cnt2 ++;
 52 }
 53 
 54 void lca_tarjan( int u , int val )
 55 {
 56     int v , x , y;
 57     vis[u] = true;
 58     dist[u] = val;
 59     father[u] = u;
 60     for( int i = Ehead[u] ; ~i ; i = edge[i].next )
 61     {
 62         v = edge[i].to;
 63         if( !vis[v] )
 64         {
 65             lca_tarjan( v , edge[i].val + val );
 66             x = find(u);
 67             y = find(v);
 68             if( x!=y )
 69             {
 70                 father[y] = x;
 71             }
 72         }
 73     }
 74     for( int i = Nhead[u] ; ~i ; i = node[i].next )
 75     {
 76         v = node[i].to; 
 77         if( vis[v] )
 78         {
 79             node[i].lca = node[i^1].lca = find(v);
 80         }
 81     }
 82 }
 83 
 84 int main()
 85 {
 86     cin.sync_with_stdio(false);
 87     int t , from , to , val , ans , id;
 88     int n , m;
 89     cin >> t;
 90     while( t-- )
 91     {
 92         init( );
 93         cin >> n >> m;
 94         cnt1 = cnt2 = 0;
 95         for( int i = 1 ; i<n ; i++ )
 96         {
 97             cin >> from >> to >> val;
 98             addEdge( from , to , val );
 99             addEdge( to , from , val );
100         }
101         for( int i = 0 ; i<m ; i++ )
102         {
103             cin >> from >> to;
104             addQueryEdge( from , to );
105             addQueryEdge( to , from );
106         }
107         lca_tarjan( 1 , 0 );
108         for( int i = 0 ; i<m ; i++ )
109         {
110             id = i * 2;
111             ans = dist[ node[id].from ] + dist[ node[id].to ] - 2*dist[ node[id].lca ];
112             cout << ans << endl;
113         }
114     }
115     return 0;
116 }