hdu 4000 Fruit Ninja 树状数组

 1 #include<iostream>
 2 #include<cstdio>
 3 #include<cstring>
 4 #include<cstdlib>
 5 #include<cmath>
 6 #include<algorithm>
 7 #define inf 0x7fffffff
 8 using namespace std;
 9 typedef long long LL;
10 const int maxn=100000+10;
11 const int MOD=100000007;
12 
13 int n,an[maxn];
14 LL x[maxn];
15 
16 int lowbit(int u) {return u&(-u); }
17 void add(int i,int dd)
18 {
19     while (i<=maxn)
20     {
21         x[i] += dd;
22         i += lowbit(i);
23     }
24 }
25 LL sum(int i)
26 {
27     LL ret=0;
28     while (i>0)
29     {
30         ret += x[i];
31         i -= lowbit(i);
32     }
33     return ret;
34 }
35 
36 int main()
37 {
38     int t,ncase=1;scanf("%d",&t);
39     while (t--)
40     {
41         scanf("%d",&n);
42         for (int i=1 ;i<=n ;i++) scanf("%d",&an[i]);
43         memset(x,0,sizeof(x));
44         LL ans=0;
45         for (int i=1 ;i<=n ;i++)
46         {
47             add(an[i],1);
48             LL temp1=sum(an[i]-1);
49             LL temp2=n-an[i]-((i-1)-temp1);
50             ans -= temp1*temp2;
51             if (temp2>=2) ans += (temp2-1)*temp2/2;
52         }
53         printf("Case #%d: %I64d\n",ncase++,ans%MOD);
54     }
55     return 0;
56 }