唉，看到这题直接想起自己的Day1，还是挺难受的，挺傻一题考试的时候怎么就没弄出来呢……
这两天CP让我给他写个题解，弄了不是很久就把这个题给弄出来了，真不知道考试的时候在干嘛。
明天就出发去北京了，祝自己APIO顺利吧。
1 /************************************************************** 2 Problem: 3528 3 User: zhuohan123 4 Language: C++ 5 Result: Accepted 6 Time:1736 ms 7 Memory:25408 kb 8 ****************************************************************/ 9 10 #include <iostream> 11 #include <cmath> 12 #include <cstdio> 13 #include <cstring> 14 #include <algorithm> 15 using namespace std; 16 const double eps=1e-7; 17 inline int getnum() 18 { 19 int ans=0,fh=1;char ch=getchar(); 20 while(ch<'0'||ch>'9'){if(ch=='-')fh*=-1;ch=getchar();} 21 while(ch>='0'&&ch<='9')ans=ans*10+ch-'0',ch=getchar(); 22 return fh*ans; 23 } 24 struct info 25 { 26 int n,x,y,x2,y2,xy; 27 info(){n=x=y=x2=y2=xy=0;} 28 info(int X,int Y){n=1;x=X;y=Y;x2=X*X;y2=Y*Y;xy=X*Y;} 29 info(int N,int X,int Y,int X2,int Y2,int XY){n=N;x=X;y=Y;x2=X2;y2=Y2;xy=XY;} 30 inline friend info operator+(info a,info b){return info(a.n+b.n,a.x+b.x,a.y+b.y,a.x2+b.x2,a.y2+b.y2,a.xy+b.xy);} 31 inline friend info operator-(info a,info b){return info(a.n-b.n,a.x-b.x,a.y-b.y,a.x2-b.x2,a.y2-b.y2,a.xy-b.xy);} 32 inline info operator+=(info b){n+=b.n;x+=b.x;y+=b.y;x2+=b.x2;y2+=b.y2;xy+=b.xy;return *this;} 33 inline double xbar(){return (double)x/(double)n;} 34 inline double ybar(){return (double)y/(double)n;} 35 inline double A(){return x2-2*xbar()*x+n*xbar()*xbar();} 36 inline double B(){return 2*ybar()*x+2*xbar()*y-2*xy-2*n*xbar()*ybar();} 37 inline double C(){return y2-2*ybar()*y+n*ybar()*ybar();} 38 inline double delta() 39 { 40 if(n==1)return 0; 41 double a=A(),b=B(),c=C(),d=sqrt(a*a+b*b+c*c-2*a*c); 42 double ans1=(a+c+d)/2,ans2=(a+c-d)/2; 43 if(ans1>ans2)swap(ans1,ans2); 44 return ans1>-eps?ans1:ans2; 45 } 46 }; 47 int n,m; 48 struct point 49 { 50 int head,f[20],deep,incir,wt; 51 info x; 52 }p[110000]; 53 struct edge{int next,to;}g[210000];int gnum; 54 void addedge(int from,int to) 55 { 56 g[++gnum].to=to;g[gnum].next=p[from].head;p[from].head=gnum; 57 g[++gnum].to=from;g[gnum].next=p[to].head;p[to].head=gnum; 58 } 59 namespace Tree 60 { 61 void dfs(int po) 62 { 63 p[po].deep=p[p[po].f[0]].deep+1; 64 for(int i=1;i<=17;i++) 65 p[po].f[i]=p[p[po].f[i-1]].f[i-1]; 66 for(int i=p[po].head;i;i=g[i].next) 67 if(g[i].to!=p[po].f[0]) 68 { 69 p[g[i].to].x+=p[po].x; 70 p[g[i].to].f[0]=po; 71 dfs(g[i].to); 72 } 73 } 74 inline int lca(int u,int v) 75 { 76 if(p[u].deep>p[v].deep)swap(u,v); 77 for(int i=17;i>=0;i--) 78 if(p[p[v].f[i]].deep>=p[u].deep)v=p[v].f[i]; 79 if(u==v)return u; 80 for(int i=17;i>=0;i--) 81 if(p[v].f[i]!=p[u].f[i])v=p[v].f[i],u=p[u].f[i]; 82 return p[v].f[0]; 83 } 84 void solve() 85 { 86 dfs(1); 87 int q=getnum(); 88 while(q--) 89 { 90 int u=getnum(),v=getnum(),l=lca(u,v); 91 printf("%.5lf ",(p[u].x+p[v].x-p[l].x-p[p[l].f[0]].x).delta()+eps); 92 } 93 } 94 } 95 namespace Circle 96 { 97 bool ins[110000]; 98 int s[110000],sr; 99 int cir[210000],cnum; 100 info cinfo[210000]; 101 inline info cirwalk(int l,int r){return cinfo[r]-cinfo[l-1];} 102 bool dfscir(int po,int from) 103 { 104 ins[s[++sr]=po]=true; 105 for(int i=p[po].head;i;i=g[i].next) 106 if(g[i].to!=from) 107 { 108 if(ins[g[i].to]) 109 { 110 while(s[sr]!=g[i].to) 111 { 112 cir[++cnum]=s[sr]; 113 p[s[sr]].incir=cnum; 114 sr--; 115 } 116 cir[++cnum]=g[i].to; 117 p[g[i].to].incir=cnum; 118 return true; 119 } 120 else if(dfscir(g[i].to,po))return true; 121 } 122 sr--; 123 ins[po]=false;return false; 124 } 125 void dfstree(int po,int wt) 126 { 127 p[po].wt=wt; 128 p[po].deep=p[p[po].f[0]].deep+1; 129 for(int i=1;i<=17;i++) 130 p[po].f[i]=p[p[po].f[i-1]].f[i-1]; 131 for(int i=p[po].head;i;i=g[i].next) 132 if(g[i].to!=p[po].f[0]&&!p[g[i].to].incir) 133 { 134 p[g[i].to].x+=p[po].x; 135 p[g[i].to].f[0]=po; 136 dfstree(g[i].to,wt); 137 } 138 } 139 inline int lca(int u,int v) 140 { 141 if(p[u].deep>p[v].deep)swap(u,v); 142 for(int i=17;i>=0;i--) 143 if(p[p[v].f[i]].deep>=p[u].deep)v=p[v].f[i]; 144 if(u==v)return u; 145 for(int i=17;i>=0;i--) 146 if(p[v].f[i]!=p[u].f[i])v=p[v].f[i],u=p[u].f[i]; 147 return p[v].f[0]; 148 } 149 void solve() 150 { 151 dfscir(1,0); 152 for(int i=1;i<=cnum;i++)dfstree(cir[i],cir[i]); 153 for(int i=1;i<=cnum;i++)cir[i+cnum]=cir[i]; 154 for(int i=1;i<=2*cnum;i++)cinfo[i]=cinfo[i-1]+p[cir[i]].x; 155 int q=getnum(); 156 while(q--) 157 { 158 int u=getnum(),v=getnum(); 159 if(p[u].wt==p[v].wt) 160 { 161 int l=lca(u,v); 162 printf("%.5lf ",(p[u].x+p[v].x-p[l].x-p[p[l].f[0]].x).delta()+eps); 163 } 164 else 165 { 166 int fu=p[u].wt,fv=p[v].wt; 167 info iu=p[u].x-p[fu].x,iv=p[v].x-p[fv].x; 168 if(p[fu].incir>p[fv].incir)swap(fu,fv); 169 info imid1=cirwalk(p[fu].incir,p[fv].incir); 170 info imid2=cirwalk(p[fv].incir,p[fu].incir+cnum); 171 printf("%.5lf ",min((iu+imid1+iv).delta(),(iu+imid2+iv).delta())+eps); 172 } 173 } 174 } 175 } 176 int main(int argc, char *argv[]) 177 { 178 //freopen("1.in","r",stdin); 179 //freopen("1.out","w",stdout); 180 n=getnum(),m=getnum(); 181 for(int i=1;i<=n;i++) 182 { 183 int x=getnum(),y=getnum(); 184 p[i].x=info(x,y); 185 } 186 for(int i=1;i<=m;i++)addedge(getnum(),getnum()); 187 if(m==n-1)Tree::solve(); 188 else Circle::solve(); 189 return 0; 190 }