CQOI2009 BZOJ1303 中位数

 1 var n,b,mid,k,I:longint;
 2     ans:int64;
 3     a:array[0..100008] of longint;
 4     f,g:array[-100008..100008] of longint;
 5 begin
 6     readln(n,b);
 7     for i:=1 to n do
 8     begin
 9         read(a[i]);
10         if b=a[i] then mid:=i;
11     end;
12     k:=1;
13     for i:=mid downto 1 do
14     begin
15         if a[i]>a[mid] then dec(k);
16         if a[i]<a[mid] then inc(k);
17         inc(f[k]);
18     end;
19     k:=1;
20     for i:=mid to n do
21     begin
22         if a[i]>a[mid] then inc(k);
23         if a[i]<a[mid] then dec(k);
24         inc(g[k]);
25     end;
26     for i:=-n to n do ans:=ans+f[i]*g[i];
27     writeln(ans);
28 end.