Jubilee

#include <bits/stdc++.h>

using namespace std;

using ll = long long;

const ll MOD   = 1e9 + 7;
const ll MAX_N = 1e6 + 123;

ll dp[MAX_N][2];

ll factorial[MAX_N];
ll inv_factorial[MAX_N];

ll binpow(ll a, ll n)
{
    if (n == 0) return 1LL;
    if (n % 2 == 0)
    {
        ll tmp = binpow(a, n / 2);
        return (tmp * tmp) % MOD;
    }
    return (a * binpow(a, n - 1)) % MOD;
}

ll ank(ll n, ll k)
{
    return (factorial[n] * inv_factorial[n - k]) % MOD;
}

int main()
{
    ios_base::sync_with_stdio(false);

    factorial[0]     = 1LL;
    inv_factorial[0] = binpow(factorial[0], MOD - 2);
    for (ll i = 1; i < MAX_N; i++)
    {
        factorial[i]     = (factorial[i - 1] * i) % MOD;
        inv_factorial[i] = binpow(factorial[i], MOD - 2);
    }

    ll n, m;
    cin >> n >> m;

    if (m == 1)
    {
        cout << 0 << '\n';
        return 0;
    }

    dp[0][0] = ank(m, 1);
    dp[0][1] = ank(m, 2);

    for (ll i = 1; i < n; i++)
    {
        dp[i][0] = 0;
        if (m - 1 >= 1)
            dp[i][0] = (dp[i][0] + (dp[i - 1][0] * ank(m - 1, 1)) % MOD) % MOD;
        if (m - 2 >= 1)
            dp[i][0] = (dp[i][0] + (dp[i - 1][1] * ank(m - 2, 1)) % MOD) % MOD;

        dp[i][1] = 0;
        if (m - 1 >= 2)
            dp[i][1] = (dp[i][1] + (dp[i - 1][0] * ank(m - 1, 2)) % MOD) % MOD;
        if (m - 2 >= 2)
            dp[i][1] = (dp[i][1] + (dp[i - 1][1] * ank(m - 2, 2)) % MOD) % MOD;
    }

    ll answer = (dp[n - 1][0] + dp[n - 1][1]) % MOD;
    cout << answer << '\n';

    return 0;
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: RUNTIME ERROR

Test 4

Verdict: RUNTIME ERROR

Test 5

Verdict: RUNTIME ERROR

Test 6

Verdict: RUNTIME ERROR

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: WRONG ANSWER

Test 10

Verdict: ACCEPTED

Test 11

Verdict: WRONG ANSWER

Test 12

Verdict: WRONG ANSWER

Test 13

Verdict: WRONG ANSWER

Test 14

Verdict: RUNTIME ERROR