题目连接：

lowbit..

1 #include
     
       2 #include
      
        3 #define ll long long 4 const int maxn=1e6+10; 5  6 int c[maxn]; 7 int a[20005]; 8 int m1[20005],m2[20005]; 9 10 int lowbit(int x)11 {12     return x&(-x);13 }14 15 int sum(int x)16 {17     int ret=0;18     while(x>0)19     {20         ret+=c[x];21         x-=lowbit(x);22     }23     return ret;24 }25 26 void add(int x,int d)27 {28     while(x
       
        =1;i--)51         {52             m2[i]=sum(a[i]);53             add(a[i],1);54         }55         ll ans=0;56         for(int i=1;i<=n;i++)57             ans+=m1[i]*1ll*(n-i-m2[i])+m2[i]*1ll*(i-m1[i]-1);58         printf("%lld\n",ans);59     }60 }