POJ 1001 (坑爹的小数高精度乘法)

小数高精度乘法


program P1001;
Type
    arr=record
        a:array[1..10000] of longint;
        len:longint;
        xs:longint;
        end;
Var
    s:ansistring;
    n,i,j,k,len:longint;
    r:arr;
Procedure relax(var c:arr);
var
   i,j:longint;
begin
   while (c.a[c.len]=0) and (c.len>1) do dec(c.len);
   if (c.len=1) and (c.a[1]=0) then begin c.xs:=0; exit; end;
   i:=1;
   while (c.a[i]=0) do inc(i);
   dec(i);
   if (i>0) then
   begin
      if (c.xs>=i) then dec(c.xs,i)
      else
      begin
         i:=c.xs;
         c.xs:=0;
      end;
      for j:=i+1 to c.len do c.a[j-i]:=c.a[j];
      dec(c.len,i);
   end;
end;
procedure prin(c:arr);
var
   i:longint;
begin
   relax(c);
   if (c.xs=0) then
   begin
      for i:=c.len downto 1 do write(c.a[i]);
      writeln;
      exit;
   end;
   if (c.xs<=c.len) then
   begin
      for i:=c.len downto c.xs+1 do write(c.a[i]);
      write('.');
      for i:=c.xs downto 1 do write(c.a[i]);
      writeln;
      exit;
   end;
   write('.');
   for i:=1 to c.xs-c.len do write('0');
   for i:=c.len downto 1 do write(c.a[i]);
   writeln;
end;
Procedure cheng(a:arr;b:arr;var c:arr);
var
   i,j:longint;
begin
   fillchar(c,sizeof(c),0);
   for i:=1 to a.len do
      for j:=1 to b.len do
      begin
         inc(c.a[i+j-1],a.a[i]*b.a[j]);
         inc(c.a[i+j],c.a[i+j-1] div 10);
         c.a[i+j-1]:=c.a[i+j-1] mod 10;
      end;
   c.len:=a.len+b.len+1;
   c.xs:=a.xs+b.xs;

   relax(c);

end;
procedure jie(a:arr;b:longint;var c:arr);
begin
   if (b=1) then c:=a
   else if (b mod 2=0) then
   begin
      jie(a,b div 2,c);
      cheng(c,c,c);
   end
   else begin
      jie(a,b div 2,c);
      cheng(c,c,c);
      cheng(c,a,c);
   end;

end;
Begin
   while (not(eof)) do
   begin
      readln(s);
      len:=length(s);
      i:=pos(' ',s);
      j:=pos('.',s);
      if j=0 then
      begin
         r.xs:=0;
         r.len:=i-1;
         for k:=1 to r.len do r.a[r.len-k+1]:=ord(s[k])-48;
      end
      else begin
      r.xs:=i-j-1;
      r.len:=i-2;
      for k:=1 to j-1 do r.a[r.len-k+1]:=ord(s[k])-48;
      for k:=j+1 to i-1 do r.a[r.len-k+2]:=ord(s[k])-48;
      end;
      relax(r);
      i:=len;
      while (s[i]<>' ') do dec(i);
      n:=0;
      for k:=i+1 to len do n:=n*10+ord(s[k])-48;
      jie(r,n,r);
      prin(r);
  end;
end.


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