BZOJ1106 [POI2007]立方体大作战tet

 1 /**************************************************************
 2     Problem: 1106
 3     User: rausen
 4     Language: C++
 5     Result: Accepted
 6     Time:164 ms
 7     Memory:1976 kb
 8 ****************************************************************/
 9  
10 #include <cstdio>
11  
12 using namespace std;
13 const int N = 100005;
14 int n, ans;
15 int a[N], BIT[N], l[N];
16  
17 inline int read(){
18     int x = 0, sgn = 1;
19     char ch = getchar();
20     while (ch < ‘0‘ || ch > ‘9‘){
21         if (ch == ‘-‘) sgn = -1;
22         ch = getchar();
23     }
24     while (ch >= ‘0‘ && ch <= ‘9‘){
25         x = x * 10 + ch - ‘0‘;
26         ch = getchar();
27     }
28     return sgn * x;
29 }
30  
31 inline int lowbit(int x){
32     return x & -x;
33 }
34  
35 inline int query(int x){
36     int res = 0;
37     for (; x; x -= lowbit(x))
38         res += BIT[x];
39     return res;
40 }
41  
42 inline void add(int x, const int del){
43     for (; x <= n; x += lowbit(x))
44         BIT[x] += del;
45 }
46  
47 int main(){
48     n = read(), n <<= 1;
49     int i;
50     for (i = 1; i <= n; ++i)
51         a[i] = read();
52     for (i = 1; i <= n; ++i)
53         if (!l[a[i]]) add(i, 1), l[a[i]] = i;
54         else{
55             ans += query(i) - query(l[a[i]]);
56             add(l[a[i]], -1);
57         }
58     printf("%d\n", ans);
59     return 0;
60 }