poj2299
树状数组
View Code
#include
<
iostream
>
#include
<
cstdio
>
#include
<
cstdlib
>
#include
<
cstring
>
#include
<
algorithm
>
using
namespace
std;
#define
maxn 500005
struct
Elem
{
int
p, v;
}s[maxn];
int
f[maxn];
int
pos[maxn];
int
ar[maxn];
bool
operator
<
(
const
Elem
&
a,
const
Elem
&
b)
{
return
a.v
<
b.v;
}
int
lowb(
int
t)
{
return
t
&
(
-
t);
}
void
add(
int
i,
int
v)
{
for
(; i
<
maxn; ar[i]
+=
v, i
+=
lowb(i));
}
int
sum(
int
i)
{
int
s
=
0
;
for
(; i
>
0
; s
+=
ar[i], i
-=
lowb(i));
return
s;
}
int
main()
{
//
freopen("t.txt", "r", stdin);
int
n;
memset(ar,
0
,
sizeof
(ar));
while
(scanf(
"
%d
"
,
&
n), n)
{
memset(ar,
0
,
sizeof
(ar));
for
(
int
i
=
0
; i
<
n; i
++
)
{
scanf(
"
%d
"
,
&
f[i]);
s[i].v
=
f[i];
s[i].p
=
i;
}
sort(s, s
+
n);
for
(
int
i
=
0
; i
<
n; i
++
)
pos[s[i].p]
=
i
+
1
;
long
long
ans
=
0
;
for
(
int
i
=
n
-
1
; i
>=
0
; i
--
)
{
ans
+=
sum(pos[i]
-
1
);
add(pos[i],
1
);
}
printf(
"
%lld\n
"
, ans);
}
return
0
;
}