Language: C++

#define _USE_MATH_DEFIMES
#include <algorithm>
#include <array>
#include <bitset>
#include <cassert>
#include <cctype>
#include <climits>
#include <clocale>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstdlib>
#include <ctime>
#include <deque>
#include <fstream>
#include <functional>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <regex>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <tuple>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>

const int MOD = 1'000'000'007;
const int INF = 1'000'000'000; //1e9
const int NIL = -1;
const long long LINF = 1'000'000'000'000'000'000; // 1e18
const long double EPS = 1E-10;

template<class T, class S> inline bool chmax(T &a, const S &b){
    if(a < b){
        a = b; return true;
    }
    return false;
}
template<class T, class S> inline bool chmin(T &a, const S &b){
    if(b < a){
        a = b; return true;
    }
    return false;
}





template<unsigned long long m> class comb_perm{
private:
    std::vector<long long> fact_inv, fact;
    int n;
public:
    comb_perm(): n(0), , fact(1), fact_inv(1){
        fact[0] = fact_inv[0] = 1;
    }
    comb_perm(int N): n(N), fact(N+1), fact_inv(N+1){
        fact[0] = fact[1] = fact_inv[0] = fact_inv[1] = 1;
        for(int i(2); i <= n; ++i) fact[i] = fact[i - 1] * i % m;
        for(int i(2); i <= n; ++i) fact_inv[i] = inv(fact[i]);
    }

    void resize(int N){
        fact.resize(N+1);
        fact_inv.resize(N+1);
        if(!n && N){
            fact[1] = fact_inv[1] = 1;
        }
        for(int i(std::max(2, n+1)); i <= N; ++i) fact[i] = fact[i - 1] * i % m;
        for(int i(std::max(2, n+1)); i <= N; ++i) fact_inv[i] = inv(fact[i], m);
        n = N;
    }

    long long power(long long a, unsigned long long b){
        long long ret(1);
        while(b){
            if(b & 1) ret = (ret * a) % m;
            a = (a * a) % m;
            b /= 2;
            if(ret < 0) ret += m;
            if(a < 0) a += m;
        }
        return ret;
    }

    long long inv(long long a){ // GCD(a, m) = 1
        return power(a, m-2);
    }

    long long permutation(int n, int r){
        if(n < r) return 0;
        if(n < 0 || r < 0) return 0;
        long long ret(fact[n]);
        ret = ret * fact_inv[n - r] % m;
        return ret;
    }

    long long combination(int n, int r){
        if(n < r) return 0;
        if(n < 0 || r < 0) return 0;
        long long ret(permutation(n, r));
        return ret * fact_inv[r] % m;
    }

    long long factorise(int a){
        return fact[a];
    }

    long long inv_factorise(int a){
        return fact_inv[a];
    }
};


int main(){
    int N, M; std::cin >> N >> M;
    comb_perm<MOD> CP(M+3);
    long long ans(0);
    for(int i(0); i <= N; ++i){
        int a((i % 2) ? -1 : 1);
        long long c(CP.combination(N, i));
        c *= CP.permutation(M-i, N-i);
        ans += a * (c % MOD);
        ans %= MOD;
        if(ans < 0) ans += MOD;
    }
    ans *= CP.permutation(M, N);
    ans %= MOD;
    std::cout << ans << std::endl;
    return 0;
}


Compiler output:
a.cc: In constructor 'comb_perm<m>::comb_perm()':
a.cc:63:24: error: expected identifier before ',' token
   63 |     comb_perm(): n(0), , fact(1), fact_inv(1){
      |                        ^