HDU2874+LCA+tarjan

可用tarjan来做。。。

  1 /*
  2 lca+tarjan
  3 */
  4 #include<stdio.h>
  5 #include<string.h>
  6 #include<stdlib.h>
  7 #include<algorithm>
  8 #include<iostream>
  9 #include<queue>
 10 #include<map>
 11 #include<math.h>
 12 using namespace std;
 13 typedef long long ll;
 14 //typedef __int64 int64;
 15 const int maxn = 10005;
 16 const int maxm = 1000005;
 17 
 18 int cnt,head[ maxn ],ex_cnt,ex_head[ maxn ];
 19 struct node{
 20     int u,next,val;
 21 }edge[ maxn<<4 ],ex_edge[ maxm<<1 ];
 22 void init(){
 23     cnt = ex_cnt = 0;
 24     memset( head,-1,sizeof( head ) );
 25     memset( ex_head,-1,sizeof( ex_head ) );
 26 }
 27 void addedge( int a,int b,int c ){
 28     edge[ cnt ].u = b;
 29     edge[ cnt ].val = c;
 30     edge[ cnt ].next = head[ a ];
 31     head[ a ] = cnt++;
 32 }
 33 void ex_addedge( int a,int b,int c ){
 34     ex_edge[ ex_cnt ].u = b;
 35     ex_edge[ ex_cnt ].val = c;
 36     ex_edge[ ex_cnt ].next = ex_head[ a ];
 37     ex_head[ a ] = ex_cnt++;
 38 }
 39 
 40 int belong[ maxn ];//记录两个点是否属于同一棵树
 41 int vis[ maxn ],dis[ maxn ],fa[ maxn ];
 42 
 43 void make_set( int x ){
 44     fa[ x ] = x;
 45 }
 46 int find( int x ){
 47     if( x==fa[x] ) return x;
 48     return fa[x] = find( fa[x] );
 49 }
 50 
 51 struct node2{
 52     int u,v;
 53 }query[ maxm ];
 54 int ans[ maxm ];//存储答案
 55 
 56 void dfs( int cur,int flag ){
 57     //if( vis[ cur ]==1 ) return ;
 58     vis[ cur ] = 1;
 59     belong[ cur ] = flag;
 60     for( int i=head[ cur ];i!=-1;i=edge[ i ].next ){
 61         if( vis[ edge[ i ].u ]==0 ){
 62             dfs( edge[ i ].u,flag );
 63         }
 64     }
 65     return ;
 66 }
 67 
 68 void tarjan_of_lca( int cur,int dist ){
 69     make_set( cur );
 70     vis[ cur ] = 1;
 71     dis[ cur ] = dist;
 72     for( int i=head[ cur ];i!=-1;i=edge[ i ].next ){
 73         int v = edge[ i ].u;
 74         if( vis[ v ]==0 ){
 75             tarjan_of_lca( v,dist+edge[ i ].val );
 76             fa[ v ] = cur;
 77         }
 78     }
 79     for( int ii=ex_head[ cur ];ii!=-1;ii=ex_edge[ ii ].next ){
 80         int v = ex_edge[ ii ].u;
 81         if( vis[ v ]==1 ){
 82             int val = ex_edge[ ii ].val;
 83                int father = find( v );
 84             ans[ val ] = dis[ cur ]+dis[ v ]-2*dis[ father ];
 85         }
 86     }
 87 } 
 88 
 89 int main(){
 90     int n,m,k;
 91     //freopen( "in.txt","r",stdin );
 92     while( scanf("%d%d%d",&n,&m,&k)==3 ){
 93         init();
 94         int a,b,c;
 95         while( m-- ){
 96             scanf("%d%d%d",&a,&b,&c);
 97             addedge( a,b,c );
 98             addedge( b,a,c );
 99         }
100         memset( vis,0,sizeof( vis ) );
101         for( int i=1;i<=n;i++ ){
102             belong[ i ] = i;
103             fa[ i ] = i;
104         }
105         int cc = 1;//cc表示树的标记
106         for( int i=1;i<=n;i++ ){
107             if( vis[ i ]==0 ){
108                 dfs( i,cc );
109                 cc++;
110             }
111         }
112         for( int i=1;i<=k;i++ ){
113             scanf("%d%d",&a,&b);
114             if( a!=b ){
115                 ex_addedge( a,b,i );
116                 ex_addedge( b,a,i );
117             }
118             else ex_addedge( a,b,i );
119             query[ i ].u = a;
120             query[ i ].v = b;
121         }
122         memset( vis,0,sizeof( vis ) );
123         for( int i=1;i<=n;i++ ){
124             if( vis[ i ]==0 ){
125                 tarjan_of_lca( i,0 );
126             }
127         }
128         for( int i=1;i<=k;i++ ){
129             if( belong[ query[i].u ]!=belong[ query[i].v ] ) printf("Not connected\n");
130             else{
131                 printf("%d\n",ans[ i ]);
132             }
133         }
134     }
135     return 0;
136 }

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