hdu 4000 Fruit Ninja

小大中+小中大= ?

#include <cstdio>
#include <cstring>
const int MAXN = 100000 + 1234;
const int mod = 100000007;
int n;
long long tree[MAXN];
long long ans[MAXN];
int a[MAXN];
inline int Lowbit(int x)
{
    return x&(-x);
}
void Update(int x, long long val)
{
    for(int i = x; i > 0; i-=Lowbit(i))
    {
        tree[i]+=val;
        tree[i] %= mod;
    }
}
long long Getsum(int x)
{
    long long temp = 0;
    for(int i = x; i <= n; i+=Lowbit(i))  temp+= tree[i];
    temp %= mod;
    return temp;
}
void Update2(int x, long long val)
{
    for(int i = x; i <= n; i+=Lowbit(i))
    {
        tree[i]+=val;
        tree[i] %= mod;
    }
}
long long Getsum2(int x)
{
    long long temp = 0;
    for(int i = x; i > 0; i-=Lowbit(i))  temp+= tree[i];
    temp %= mod;
    return temp;
}
int main()
{
    int T,cas=1;
    scanf("%d", &T);
    while(T--)
    {
        scanf("%d", &n);
        for(int i = 1; i <= n; i++)  scanf("%d", &a[i]);
        long long sum = 0;
        memset(tree, 0, sizeof(tree));
        for(int i = n; i >= 1; i--)
        {
            ans[i] = Getsum(a[i]);
            if(ans[i]  == 2) sum += 1;
            else
            {
                sum += (ans[i] - 1) * ans[i] / 2;
            }

            sum = sum % mod;
            Update(a[i], 1);
            //printf("sum=%d\n", sum);
        }

      // printf("sum=%d\n", sum);
        memset(tree, 0, sizeof(tree));
        long long sum2 = 0;
        for(int i = 1; i <= n; i++)
        {
            sum2 += ans[i] * Getsum2(a[i]);
            sum2 %= mod;
            Update2(a[i], 1);
            //printf("sum2=%d\n",sum2);
        }

        long long tans = ((sum - sum2) % mod + mod) % mod;
        printf("Case #%d: %I64d\n",cas++, tans);
    }
    return 0;
}