[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 li<re do  begin    mid:=(li+re)div 2;    if check(mid) then li:=mid+1    else re:=mid;  end;  writeln(li-1);end.