NOIP模板

LCA

倍增

1.不要忘记dfs后调用work

2.注意枚举2^i时要包含0，注意顺序

procedure add(x,y,v:longint);
var p:point;
begin
  new(p); p^.x:=y; p^.v:=v; p^.next:=a[x]; a[x]:=p;
end;
procedure dfs(x,k:longint);
var p:point;
begin
  new(p); p:=a[x];  f[0,x]:=k; deep[x]:=deep[k]+1;
  while p<>nil do
   begin
     if p^.x<>k then
       begin s[p^.x]:=s[x]+p^.v; dfs(p^.x,x); end;p:=p^.next;
   end;
end;
procedure work;
var i,j:longint;
begin
  for i:=0 to trunc(ln(n)/ln(2))-1 do
   for j:=1 to n do
    f[i+1,j]:=f[i,f[i,j]];
end;
function lca(x,y:longint):longint;
var i,t:longint;
begin
  if deep[x]<deep[y] then begin t:=x; x:=y; y:=t; end;
  for i:=0 to trunc(ln(n)/ln(2)) do
   if ((deep[x]-deep[y])>>i) and 1=1 then x:=f[i,x];
  if x=y then exit(x);
  for i:=trunc(ln(n)/ln(2)) downto 0 do
   if f[i,x]<>f[i,y] then
    begin x:=f[i,x]; y:=f[i,y]; end;
  exit(f[0,x]);
end;   

二分图

染色

function dfs(x,c:longint):boolean;
var i,y:longint; p:point;
begin
  color[x]:=c;
  new(p);p:=w[x];
  while p<>nil do
   begin
     y:=p^.x;
     if color[y]=c then exit(false);
     if (color[y]=0)and(not dfs(y,3-c)) then exit(false);
     p:=p^.next;
   end;
  exit(true);
end;
procedure work;
var i:longint;
begin
  for i:=1 to n do color[i]:=0;
  for i:=1 to n do
   if color[i]=0 then
    if not dfs(i,1) then
     begin flag:=false; exit; end;
end;