3175: [Tjoi2013]攻击装置

所有的白格向能攻击到的黑格连单向边，然后最大独立集就行了。细节看代码吧。

RunID	User	Problem	Result	Memory	Time	Language	Code_Length	Submit_Time
411274	lbz007	3175	Accepted	20068 kb	2212 ms	Pascal/Edit	1637 B	2013-05-13 17:19:41

const
  x:array[1..8]of longint=(-1,-2,1,2,-1,-2,1,2);
  y:array[1..8]of longint=(-2,-1,-2,-1,2,1,2,1);
var
  n,i,j,k,numa,ans,ee:longint;
  b,link,e,head,next:Array[1..1000000]of longint;
  d,a:Array[1..200,1..200]of longint;
  c:char;
procedure add(u,v:longint);
  begin
  inc(ee);next[ee]:=head[u];head[u]:=ee;e[ee]:=v;
  //inc(ee);next[ee]:=head[v];head[v]:=ee;e[ee]:=u ;
  end;
function find(x:longint):boolean;
  var j:longint;
  begin
  j:=head[x];
  while j<>0 do
    begin
    if b[e[j]]<>i then
      begin
      b[e[j]]:=i;
      if (link[e[j]]=0) or (find(link[e[j]])) then
        begin
        link[e[j]]:=x;
        exit(true);
        end;
      end;
    j:=next[j];
    end;
  exit(false);
end;
begin
  readln(n);
  for i:=1 to n do
    begin
    for j:=1 to n do
      begin
      read(c);if c='0' then inc(numa);
      a[i,j]:=ord(c)-ord('0');
      end;
    readln;
    end;
  for i:=1 to n do
    for j:=1 to n do
      begin inc(k);d[i,j]:=k;end;
  for i:=1 to n do
    for j:=1 to n do
      if (a[i,j]=0)and((i+j) mod 2=0) then
        for k:=1 to 8 do
          if (i+x[k]>0)and(i+x[k]<=n)and(j+y[k]>0)and(j+y[k]<=n)then
            if a[i+x[k],j+y[k]]=0 then
              add(d[i,j],d[i+x[k],j+y[k]]);
 
  for k:=1 to n do
    for j:=1 to n do
      if (k+j) mod 2=0 then
        if a[k,j]=0 then
          begin
          i:=d[k,j];
          if find(i) then inc(ans);
          end;
  writeln(numa-ans);
end.