随笔 - 540  文章 - 0 评论 - 39 trackbacks - 0

其实这道题是和bzoj1787一样的
但我用bzoj1787MLE了,于是正好练一下树上倍增

  1 type node=record
  2        po,next:longint;
  3      end;
  4 
  5 var w:array[0..1000010] of node;
  6     anc:array[0..500005,0..20] of longint;
  7     dep,fa,p:array[0..500005] of longint;
  8     v:array[0..500005] of boolean;
  9     t,len,x,y,z,a,b,c,i,n,m:longint;
 10 
 11 procedure add(x,y:longint);
 12   begin
 13     inc(len);
 14     w[len].po:=y;
 15     w[len].next:=p[x];
 16     p[x]:=len;
 17   end;
 18 
 19 procedure swap(var a,b:longint);
 20   var c:longint;
 21   begin
 22     c:=a;
 23     a:=b;
 24     b:=c;
 25   end;
 26 
 27 procedure dfs(x:longint);
 28   var i,y:longint;
 29   begin
 30     v[x]:=true;
 31     i:=p[x];
 32     while i<>0 do
 33     begin
 34       y:=w[i].po;
 35       if not v[y] then
 36       begin
 37         fa[y]:=x;
 38         dep[y]:=dep[x]+1;
 39         dfs(y);
 40       end;
 41       i:=w[i].next;
 42     end;
 43   end;
 44 
 45 procedure prework;
 46   var i,j,h:longint;
 47   begin
 48     fillchar(anc,sizeof(anc),255);
 49     h:=0;
 50     for i:=1 to n do
 51     begin
 52       anc[i,0]:=fa[i];
 53       if dep[i]>h then h:=dep[i];
 54     end;
 55     t:=trunc(ln(h)/ln(2));
 56     for j:=1 to t do
 57       for i:=1 to n do
 58       begin
 59         b:=anc[i,j-1];
 60         if anc[b,j-1]<>-1 then anc[i,j]:=anc[b,j-1];
 61       end;
 62   end;
 63 
 64 function lca(x,y:longint):longint;
 65   var i,p:longint;
 66   begin
 67     if dep[x]<dep[y] then swap(x,y);
 68     if dep[x]<>dep[y] then
 69     begin
 70       p:=trunc(ln(dep[x])/ln(2));
 71       for i:=p downto 0 do
 72         if dep[x]-1 shl i>=dep[y] then
 73         begin
 74           x:=anc[x,i];
 75           if dep[x]=dep[y] then break;
 76         end;
 77     end;
 78 
 79     if x=y then exit(y);
 80     p:=trunc(ln(dep[x])/ln(2));
 81     for i:=p downto 0 do
 82       if (anc[x,i]<>-1) and (anc[x,i]<>anc[y,i]) then
 83       begin
 84         x:=anc[x,i];
 85         y:=anc[y,i];
 86       end;
 87     exit(fa[x]);
 88   end;
 89 
 90  begin
 91   readln(n,m);
 92   for i:=1 to n-1 do
 93   begin
 94     readln(x,y);
 95     add(x,y);
 96     add(y,x);
 97   end;
 98   fa[1]:=-1;
 99   dfs(1);
100   prework;
101   for i:=1 to m do
102   begin
103     readln(x,y,z);
104     a:=lca(x,y);
105     b:=lca(x,z);
106     c:=lca(y,z);
107     if a=b then
108       writeln(c,' ',dep[y]+dep[z]-2*dep[c]+dep[c]+dep[x]-2*dep[lca(x,c)])
109     else if a=c then
110       writeln(b,' ',dep[x]+dep[z]-2*dep[b]+dep[b]+dep[y]-2*dep[lca(y,b)])
111     else if b=c then
112       writeln(a,' ',dep[x]+dep[y]-2*dep[a]+dep[a]+dep[z]-2*dep[lca(z,a)])
113   end;
114 end.
115 
116  
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posted on 2014-10-25 22:12  acphile  阅读(68)  评论(0编辑  收藏