[BZOJ5055]膜法师

#include <cstdio>
#include <algorithm>
using namespace std;
typedef long long ll;
const int maxn = 300000 + 10;
const ll mod = 19260817;
int n, a[maxn];
int ref[maxn], num[maxn], num_cnt;
ll c1[maxn] = {0}, c2[maxn] = {0};
inline void Update(ll *arr, int pos, int val){
    for(int i = pos; i <= n; i += i & -i) arr[i] = (arr[i] + val) % mod;
}
inline ll Query(ll *arr, int pos){
    ll s = 0;
    for(int i = pos; i; i -= i & -i) s = (s + arr[i]) % mod;
    return s;
}
ll f[maxn], g[maxn];
int main(){
    scanf("%d", &n);
    for(int i = 1; i <= n; i++){
        scanf("%d", a + i);
        num[i] = a[i];
    }
    sort(num + 1, num + n + 1);
    num_cnt = unique(num + 1, num + n + 1) - (num + 1);
    for(int t, i = 1; i <= n; i++){
        t = lower_bound(num + 1, num + num_cnt + 1, a[i]) - num;
        ref[t] = a[i] % mod;
        a[i] = t;
    }
    for(int i = 1; i <= n; i++){
        f[i] = Query(c1, a[i] - 1);
        Update(c1, a[i], ref[a[i]]);
    }
    for(int i = n; i; i--){
        g[i] = Query(c2, n) - Query(c2, a[i]);
        if(g[i] < 0) g[i] += mod;
        Update(c2, a[i], ref[a[i]]);
    }
    ll ans = 0;
    for(int i = 1; i <= n; i++)
        ans = (ans + f[i] * g[i] % mod * ref[a[i]]) % mod;
    printf("%lld\n", ans);
    return 0;
}