[BZOJ2196]Brownie Slicing 二分答案

二维的二分答案。
代码：

var
  r,c,a,b,i,j,li,re,mid:longint;
  d,s:array[0..510,0..510]of longint;
function cal(x1,y1,x2,y2:longint):longint;
begin
  exit(s[x2,y2]-s[x2,y1-1]-s[x1-1,y2]+s[x1-1,y1-1]);
end;
function check(x:longint):boolean;
var
  i,j,lasta,lastb,na,nb:longint;
begin
  lasta:=1;
  for na:=1 to a do
  begin
    for i:=lasta to r+1 do
    begin
      lastb:=1;
      for nb:=1 to b do
      begin
        for j:=lastb to c+1 do
          if cal(lasta,lastb,i,j)>=x then break;
        lastb:=j+1;
        if lastb>c then break;
      end;
      if (nb=b)and(lastb<=c+1) then break;
    end;
    lasta:=i+1;
    if lasta>r then break;
  end;
  exit((na=a)and(lasta<=r+1));
end;

begin
  readln(r,c,a,b);
  for i:=1 to r do
    for j:=1 to c do
    begin
      read(s[i,j]);
      s[i,j]:=s[i,j]+s[i-1,j]+s[i,j-1]-s[i-1,j-1];
    end;
  li:=0;
  re:=1000000000;
  while lido
  begin
    mid:=(li+re)div 2;
    if check(mid) then li:=mid+1
    else re:=mid;
  end;
  writeln(li-1);
end.