This submission is migrated from previous version of oj.uz, which used different machine for grading. This submission may have different result if resubmitted.
#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];
void solve() {
for (int i = 2; i <= 4; i++) {
POW[i][0] = 1;
for (int j = 1; j < 300005; j++)
POW[i][j] = (ll)POW[i][j-1]*i%mod;
}
ll ans = 0;
for (int a = 2; a < n; a++)
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]*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;
}
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 = (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 (stderr)
w.cpp:46:6: warning: ISO C++ forbids declaration of 'main' with no type [-Wreturn-type]
46 | main() {
| ^
w.cpp: In function 'int main()':
w.cpp:85:6: warning: unused variable 'a' [-Wunused-variable]
85 | int a[2] = {};
| ^
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