Codeforces 629 E. Famil Door and Roads

  1 #include<iostream>
  2 #include<cstdio>
  3 #include<algorithm>
  4 #include<vector>
  5 #include<cstdlib>
  6 #include<cmath>
  7 #include<cstring>
  8 using namespace std;
  9 #define maxn 200010
 10 #define llg long long 
 11 #define yyj(a) freopen(a".in","r",stdin),freopen(a".out","w",stdout);
 12 llg n,m,T;
 13 llg sall[maxn],sdown[maxn],deep[maxn],f[maxn][21],size[maxn];
 14 vector<llg>a[maxn];
 15 
 16 inline llg getint()
 17 {
 18        llg w=0,q=0; char c=getchar();
 19        while((c<‘0‘ || c>‘9‘) && c!=‘-‘) c=getchar(); if(c==‘-‘) q=1,c=getchar(); 
 20        while (c>=‘0‘ && c<=‘9‘) w=w*10+c-‘0‘, c=getchar(); return q ? -w : w;
 21 }
 22 
 23 void dfs1(llg x,llg fa)
 24 {
 25     llg w=a[x].size(),v;
 26     deep[x]=deep[fa]+1; f[x][0]=fa;
 27     size[x]=1;
 28     for (llg i=0;i<w;i++)
 29     {
 30         v=a[x][i];
 31         if (v==fa) continue;
 32         dfs1(v,x);
 33         size[x]+=size[v];
 34         sdown[x]+=sdown[v]+size[v];
 35     }
 36 }
 37 
 38 void dfs2(llg x,llg fa)
 39 {
 40     llg w=a[x].size(),v;
 41     for (llg i=0;i<w;i++)
 42     {
 43         v=a[x][i];
 44         if (v==fa) continue;
 45         sall[v]=sall[x]+n-2*size[v];
 46         dfs2(v,x);
 47     }
 48 }
 49 
 50 void init()
 51 {
 52     llg x,y;
 53     cin>>n>>T;
 54     for (llg i=1;i<n;i++)
 55     {
 56         x=getint(),y=getint();
 57         a[x].push_back(y),a[y].push_back(x);
 58     }
 59     deep[1]=1;
 60     dfs1(1,0);
 61     sall[1]=sdown[1];
 62     dfs2(1,0);
 63     for (llg j=1;j<=20;j++)
 64         for (llg i=1;i<=n;i++)
 65             f[i][j]=f[f[i][j-1]][j-1];
 66 }
 67 
 68 llg find(llg x,llg y)
 69 {
 70     for (llg i=20;i>=0;i--)
 71         if (deep[f[x][i]]>=deep[y])
 72             x=f[x][i];
 73     if (x==y) return x;
 74     for (llg i=20;i>=0;i--)
 75         if (f[x][i]!=f[y][i])
 76             x=f[x][i],y=f[y][i];
 77     return f[x][0];
 78 }
 79 
 80 llg dis(llg x,llg y) 
 81 {
 82     return deep[x]+deep[y]-deep[find(x,y)]*2;
 83 }
 84 
 85 llg up(llg x,llg res)
 86 {
 87     for (llg i=20;i>=0;i--)
 88         if (res>=(1<<i))
 89         {
 90             x=f[x][i];
 91             res-=(1<<i);
 92         }
 93     return x;
 94 }
 95 
 96 int main()
 97 {
 98     yyj("tree");
 99     init();
100     while (T--)
101     {
102         llg x,y;
103         x=getint(),y=getint();
104         if (deep[x]<deep[y]) swap(x,y);
105         double ans=dis(x,y)+1;
106         if (find(x,y)!=y)
107         {
108             ans+=(double)sdown[x]/(double)size[x]+(double)sdown[y]/(double)size[y];
109         }
110         else
111         {
112             llg ne=up(x,deep[x]-deep[y]-1);
113             ans+=(double)sdown[x]/(double)size[x]+(double)(sall[y]-sdown[ne]-size[ne])/(double)(n-size[ne]);
114         }
115         printf("%.9lf\n",ans);
116     }
117     return 0;
118 }