#include<bits/stdc++.h>
#define ll long long
#define pb push_back
#define pii pair<int,int>
#define vi vector<int>
#define fi first
#define se second
#define all(x) (x).begin(),(x).end()
using namespace std;
const int mod = 1e9+7;
int cnt[1000005],arr[300005],n;
int POW[5][300005],IN[5][300005],sum[5][300005];
int pw(int a,int n) {
int y = 1;
for (;n;n/=2) {
if (n&1) y = (ll)y*a%mod;
a = (ll)a*a%mod;
}
return y;
}
void solve() {
for (int i = 2; i <= 4; i++) {
POW[i][0] = sum[i][0] = 1;
for (int j = 1; j < 300005; j++)
POW[i][j] = (ll)POW[i][j-1]*i%mod,
sum[i][j] = (sum[i][j-1] + POW[i][j])%mod;
}
for (int i = 2; i <= 4; i++) {
IN[i][0] = 1;
IN[i][1] = pw(i,mod-2);
for (int j = 2; j < 300005; j++)
IN[i][j] = (ll)IN[i][j-1]*IN[i][1]%mod;
}
ll ans = 0;
for (int a = 2; a < n; a++) {
ll z = (ll)(sum[2][n-1] - sum[2][a])*POW[2][n]%mod*IN[4][a+1]%mod;
z-= (ll)IN[3][a+1]*(sum[3][n-1] - sum[3][a])%mod;
z%=mod;
z= z*(POW[2][a-2] - 1)%mod;
ans = ans + z;
}
/* for (int mx = a+1; mx <= n; mx++) {
ll z = (ll)(POW[2][a-2] - 1)*POW[4][mx-a-1]%mod;
z = z*POW[2][n-mx]%mod;
z -= (ll)(POW[2][a-2]-1)*POW[3][mx-a-1]%mod;
z = (z%mod + mod)%mod;
ans += z;
// ans %= mod;
}*/
for (int a = 2; a < n; a++) {
/*for (int mx = a+1; mx < n; mx++) {
ans += (ll)POW[4][mx-a-1]*POW[2][n-mx]%mod;
ans -= POW[3][mx-a-1]*2LL%mod;
}*/
ll z = (ll)(sum[2][n-1] - sum[2][a])*POW[2][n]%mod*IN[4][a+1]%mod;
z-= (ll)(sum[3][n-1] - sum[3][a])*IN[3][a+1]*2%mod;
z += (ll)(sum[2][n-1] - sum[2][a])*IN[2][a+1]%mod;
z%=mod;
ans += z;
int mx = n;
ans += (ll)POW[4][mx - a - 1]*POW[2][n-mx]%mod;
ans -= POW[3][mx-a-1]*2LL%mod;
ans += POW[2][mx-a-1];
}
ans*=2;
ans = (ans%mod + mod)%mod;
cout << ans;
exit(0);
}
main() {
ios::sync_with_stdio(0);
cin.tie(0);
cin >> n;
for (int i = 0; i< n; i++) {
cin >> arr[i];
cnt[arr[i]]++;
}
sort(arr,arr+n);
reverse(arr,arr+n);
if (arr[n-1] == arr[0]) {
cout << 0;
return 0;
}
int diff= 1;
for (int i = 1; i <= 1000000; i++) {
if (cnt[i] > 1) diff= 0;
}
if (diff) solve();
for (int i = 1; i <= n; i++) {
if (arr[i] != arr[i-1]) {
ll left = i;
ll right = n - left;
if (left < 3 || right < 2) {
cout << 0;
return 0;
}
ll ans = 0;
for (int i = 1; i <= left - 2; i++)
ans += (left - i - 1);
ans *= right - 1;
cout << ans%(1000000007);
return 0;
}
}
int a[2] = {};
int c= 0;
ll ans = 1;
for (int i = 1; i <= 1000000; i++) {
if (cnt[i]) {
c++;
ans*=(cnt[i] - 1);
}
}
cout << ans*(c/2);
}
Compilation message
w.cpp:75:6: warning: ISO C++ forbids declaration of 'main' with no type [-Wreturn-type]
75 | main() {
| ^
w.cpp: In function 'int main()':
w.cpp:114:6: warning: unused variable 'a' [-Wunused-variable]
114 | int a[2] = {};
| ^
| # |
결과 |
실행 시간 |
메모리 |
Grader output |
| 1 |
Correct |
2 ms |
384 KB |
Output is correct |
| 2 |
Correct |
2 ms |
384 KB |
Output is correct |
| 3 |
Correct |
8 ms |
512 KB |
Output is correct |
| 4 |
Correct |
29 ms |
1536 KB |
Output is correct |
| # |
결과 |
실행 시간 |
메모리 |
Grader output |
| 1 |
Incorrect |
18 ms |
10880 KB |
Output isn't correct |
| 2 |
Incorrect |
18 ms |
11008 KB |
Output isn't correct |
| 3 |
Incorrect |
27 ms |
14968 KB |
Output isn't correct |
| 4 |
Incorrect |
42 ms |
15224 KB |
Output isn't correct |
| 5 |
Incorrect |
61 ms |
13688 KB |
Output isn't correct |
| 6 |
Incorrect |
96 ms |
15992 KB |
Output isn't correct |
| # |
결과 |
실행 시간 |
메모리 |
Grader output |
| 1 |
Incorrect |
2 ms |
384 KB |
Output isn't correct |
| 2 |
Incorrect |
2 ms |
384 KB |
Output isn't correct |
| 3 |
Incorrect |
2 ms |
384 KB |
Output isn't correct |
| 4 |
Incorrect |
2 ms |
384 KB |
Output isn't correct |
| 5 |
Incorrect |
2 ms |
384 KB |
Output isn't correct |
| 6 |
Incorrect |
3 ms |
384 KB |
Output isn't correct |
| 7 |
Incorrect |
4 ms |
768 KB |
Output isn't correct |
| 8 |
Incorrect |
16 ms |
1152 KB |
Output isn't correct |
| 9 |
Incorrect |
30 ms |
1152 KB |
Output isn't correct |
| 10 |
Incorrect |
76 ms |
5472 KB |
Output isn't correct |
