历届试题 小朋友排队

 1 #include<iostream>
 2 #include<memory.h>
 3 #define MAX 1000010
 4 #define N 100010
 5 using namespace std;
 6 int C1[MAX],C2[MAX],b[MAX];
 7 int num[N] , i;
 8 long long total[N],ans;
 9 
10 int lowbit(int x)
11 {
12     return x&(-x);
13 }
14 
15 void add(int pos,int num,int *C)
16 {
17     while(pos<=MAX)
18     {
19         C[pos]+=num;
20         pos+=lowbit(pos);
21     }
22 }
23 
24 int Sum(int pos,int *C)
25 {
26     int sum=0;
27     while(pos>0)
28     {
29         sum+=C[pos];
30         pos-=lowbit(pos);
31     }
32     return sum;
33 }
34 
35 
36 void init()
37 {
38     total[0]=0;
39     for(i=1;i<=N;i++)
40     {
41         total[i]=total[i-1]+i;
42     }
43 }
44 
45 int main()
46 {
47     init();
48     memset(C1,0,sizeof(C1));
49     memset(C2,0,sizeof(C2));
50     int n;
51     cin>>n;
52     for(i=0;i<n;i++)
53     {
54         cin>>num[i];
55         add(num[i]+1,1,C1);
56         b[i]=i-Sum(num[i],C1);
57         b[i]=b[i]-(Sum(num[i]+1,C1)-Sum(num[i],C1)-1);
58     }
59     for(i=n-1;i>=0;i--)
60     {
61         add(num[i]+1,1,C2);
62         b[i]=b[i]+Sum(num[i],C2);
63         
64     }
65     ans=0;
66     for(i=0;i<n;i++)
67     {
68         ans+=total[b[i]];
69     }
70     cout<<ans<<endl;
71     return 0;
72  }