2016弱校联盟十一专场10.2——Floyd-Warshall

 1 #include<cstdio>
 2 #include<algorithm>
 3 #include<cstring>
 4 #define F(i,a,b) for(int i=a;i<=b;i++)
 5 #define mst(a,b) memset(a,b,sizeof(a))
 6 using namespace std;
 7 typedef pair<int,int>P;
 8 
 9 const int N=1e5+200,DEG=18;
10 int g[N],v[N*2],nxt[N*2],ed,n,m,q,eed,cnt,id[N],Q[N];
11 int dep[N],fa[N][DEG],dfn[N],idx,d[201][N];
12 P vec[N];
13 bool vis[N];
14 
15 inline void adg(int x,int y){v[++ed]=y,nxt[ed]=g[x],g[x]=ed;}
16 inline void up(int &a,int b){if(a>b)a=b;}
17 
18 void dfs(int u=1,int pre=0)
19 {
20     dep[u]=dep[pre]+1,fa[u][0]=pre,dfn[u]=++idx;
21     F(i,1,DEG-1)fa[u][i]=fa[fa[u][i-1]][i-1];
22     for(int i=g[u];i;i=nxt[i])if(!dfn[v[i]])dfs(v[i],u);
23     else if(v[i]!=pre&&dfn[v[i]]<dfn[u])vec[++eed]=P(u,v[i]);
24 }
25 
26 int LCA(int a,int b){
27     if(dep[a]>dep[b])a^=b,b^=a,a^=b;
28     if(dep[a]<dep[b])F(i,0,DEG-1)if((dep[b]-dep[a])&(1<<i))b=fa[b][i];
29     if(a!=b)for(int i=DEG-1;i<0?a=fa[a][0]:0,i>=0;i--)
30     if(fa[a][i]!=fa[b][i])a=fa[a][i],b=fa[b][i];
31     return a;
32 }
33 
34 void bfs(int *d,int S)
35 {
36     mst(vis,0);
37     int head=1,tail=0,now;
38     Q[++tail]=S,vis[S]=1,d[S]=0;
39     while(head<=tail)for(int i=g[now=Q[head++]];i;i=nxt[i])
40     if(!vis[v[i]])vis[v[i]]=1,d[v[i]]=d[now]+1,Q[++tail]=v[i];
41 }
42 
43 int main()
44 {
45     while(~scanf("%d%d%d",&n,&m,&q))
46     {
47         int x,y;ed=idx=eed=cnt=0;
48         mst(g,0),mst(dfn,0),mst(fa,0),mst(id,0);
49         F(i,1,m)scanf("%d%d",&x,&y),adg(x,y),adg(y,x);
50         dfs();
51         F(i,1,eed)
52         {
53             if(!id[vec[i].first])id[vec[i].first]=++cnt,bfs(d[cnt],vec[i].first);
54             if(!id[vec[i].second])id[vec[i].second]=++cnt,bfs(d[cnt],vec[i].second);
55         }
56         F(i,1,q)
57         {
58             scanf("%d%d",&x,&y);
59             int ans=dep[x]+dep[y]-2*dep[LCA(x,y)];
60             F(j,1,eed)
61             {
62                 int u=id[vec[j].first],v=id[vec[j].second];
63                 up(ans,d[u][x]+d[v][y]+1),up(ans,d[v][x]+d[u][y]+1);
64             }
65             printf("%d\n",ans);
66         }
67     }
68     return 0;
69 }