为什么 m downto 就可以ac？~~~

自己写的自己都不明白~~0.0




program lonely;
  var
    p,d,temp,n,m,z,i,j,k,maxv,ans1,ans2:longint;
    ans3:ansistring;
    ss:string;
    g:array[0..30,0..1000] of string;
    h,f:array[0..30,0..1000] of longint;
    sub,sum:array[0..3000] of longint;
  procedure print;
    var
      t1,t2:longint;
    begin
      t1:=(ans1+ans2) div 2;
      t2:=(ans2-ans1) div 2;
      writeln('Best jury has value ',t1,' for prosecution and value ',t2,' for defence:');
      writeln(ans3);
    end;
  begin
    while not eof do
      begin
        inc(z);
        read(n,m);
        if (n=0)and(m=0) then break;
        writeln('Jury #',z);
        temp:=20*m;
        fillchar(f,sizeof(f),255);
        fillchar(h,sizeof(h),0);
        for i:=0 to 30 do
          for j:=0 to 1000 do
            g[i,j]:='';
        maxv:=0;
        fillchar(sub,sizeof(sub),0);
        fillchar(sum,sizeof(sum),0);
        for i:=1 to n do
          begin
            read(p,d);
            sub[i]:=p-d+20;
            sum[i]:=p+d;
            inc(maxv,sub[i]);
          end;
        f[0,0]:=0;
        for j:=1 to n do
          for i:=m downto 1 do   //   求解！！！！！！
            for k:=maxv-sub[j] downto 0 do
              if (f[i-1,k]<>-1)and(h[i-1,k]<j) then
                if (f[i-1,k]+sum[j]>f[i,k+sub[j]])and(k+sub[j]<=maxv) then
                  begin
                    f[i,k+sub[j]]:=f[i-1,k]+sum[j];
                    str(j,ss);
                    g[i,k+sub[j]]:=g[i-1,k]+' '+ss;
                    h[i,k+sub[j]]:=j;
                  end;
        ans1:=maxlongint shr 1;
        ans2:=0;
        for i:=0 to maxv do
          if (f[m,i]<>-1) then
            if (abs(i-temp)<abs(ans1))or((abs(ans1)=abs(i-temp))and(f[m,i]>=ans2)) then
              begin
                ans1:=i-temp;
                ans2:=f[m,i];
                ans3:=g[m,i];
              end;
        print;
        writeln;
      end;
  end.