Language: C++

#include <bits/stdc++.h>
#include <random>

using namespace std;

typedef unsigned long long ull;
typedef long long ll;
typedef double ld;
//#define ll __int128
//#define int ll
//#define int ll
//#define char ll
#define double ld
typedef vector<char> vc;
typedef vector<vc> vvc;
typedef vector<vvc> vvvc;
typedef pair<int, int> pii;
typedef pair<pii, pii> piii;
typedef pair<ll, ll> pll;
typedef vector<int> vi;
typedef vector<pii> vpi;
typedef vector<vi> vvi;
typedef vector<vvi> vvvi;
typedef vector<short> vs;
typedef vector<vs> vvs;
typedef vector<vvs> vvvs;
typedef vector<ll> vl;
typedef vector<vl> vvl;
typedef vector<vvl> vvvl;
typedef vector<ld> vld;
typedef vector<vld> vvld;
typedef vector<vvld> vvvld;
typedef vector<string> vst;
typedef vector<vst> vvst;
typedef pair<ld, ld> pld;

#define inmin(a, b) a = min(a, (b))
#define inmax(a, b) a = max(a, (b))
#define ALL(a) a.begin(),a.end()
#define RALL(a) a.rbegin(),a.rend()
#define sqr(x) ((x) * (x))
#define fori(i, n) for(int i = 0; i < int(n); ++i)
#define SZ(a) ((int)((a).size()))
#define triple(T) tuple<T, T, T>
#define quad(T) tuple<T, T, T, T>
#define watch(x) cerr << (#x) << " = " << (x) << endl;

#ifdef MAX_HOME
#define cerr cout
#else
#define cerr if (false) cerr
#endif

const double PI = 2 * acos(0.0);
//#define rand shittttty_shit
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
mt19937_64 rng_64(chrono::steady_clock::now().time_since_epoch().count());

const string DIGITS = "0123456789";
const string ALPH = "abcdefghijklmnopqrstuvwxyz";


template<class T0, class T1>
inline ostream &operator<<(ostream &out, pair<T0, T1> &a) {
    return out << "{" << a.first << ", " << a.second << "}";
}

template<class T0, class T1>
inline istream &operator>>(istream &in, pair<T0, T1> &a) {
    return in >> a.first >> a.second;
}

template<class T0, class T1, class T2>
inline ostream &operator<<(ostream &out, tuple<T0, T1, T2> &a) {
    return out << "{" << get<0>(a) << ", " << get<1>(a) << ", " << get<2>(a) << "}";
}

template<class T0, class T1, class T2, class T3>
inline ostream &operator<<(ostream &out, tuple<T0, T1, T2, T3> &a) {
    return out << "{" << get<0>(a) << ", " << get<1>(a) << ", " << get<2>(a) << ", " << get<3>(a) << "}";
}

template<class T>
inline ostream &operator<<(ostream &out, vector<T> &a) {
    out << "[";
    fori (i, a.size())out << a[i] << vector<string>{", ", "]  "}[i + 1 == a.size()];
    return out;
}


void smain();


signed main() {
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
#ifdef MAX_HOME
    freopen("input.txt", "r", stdin);
    clock_t start = clock();
#endif
    cout << setprecision(12) << fixed;
    smain();
#ifdef MAX_HOME
    cout << "\n\nTOTAL EXECUTION TIME: " << float(clock() - start) / CLOCKS_PER_SEC << endl;
#endif
    return 0;
}
const int M = 998244353;
int pw(int a,int n=M-2){
    int ret = 1;
    while (n) {
        if (n & 1)
            ret = (ll) ret * a % M;
        a = (ll) a * a % M;
        n >>= 1;
    }
    return ret;
}
const int N = 3030;
int dp[N][N];
int sum1[N][N];
int sum2[N][N];
int inv[N];
void insum(int &a,int b){
	a=(a+b<M?a+b:a+b-M);
}
void smain(){
	int a,b,c,d;
	cin>>a>>b>>c>>d;
	int n=c-a;
	int m=d-b;
	for(int i=0;i<N;i++){
		inv[i]=pw(i);
	}
	for(int i=0;i<N;i++){
		dp[i][0]=pw(b,i);
		sum2[i][0]=(ll)dp[i][0]*pw(pw(i+a-1,0))%M;
	}
	for(int j=0;j<N;j++){
		dp[0][j]=pw(a,j);
		sum1[0][j]=(ll)dp[0][j]*pw(pw(j+b-1,0))%M;
	}
	dp[0][0] = 1;
	for (int i = 1; i <= n; ++i) {
		for (int j = 1; j <= m; ++j) {
			dp[i][j] = (ll)dp[i - 1][j - 1] * (i + a - 1) % M * (j + b - 1) % M;
			int cur = (ll) sum1[i - 1][j] * pw(j + b - 1, i - 1) % M;
			insum(dp[i][j], cur);
			cur = (ll) sum2[i][j - 1] * pw(i + a - 1, j - 1) % M;
			insum(dp[i][j], cur);
			sum1[i][j] = (ll) dp[i][j] * pw(inv[j + b - 1], i) % M;
			sum2[i][j] = (ll) dp[i][j] * pw(inv[i + a - 1], j) % M;
			if (i) {
				insum(sum1[i][j], sum1[i - 1][j]);
			}
			if (j) {
				insum(sum2[i][j], sum2[i][j - 1]);
			}
		}
	}
	cout<<dp[n][m];
	return 0;
}


Compiler output:
a.cc: In function 'void smain()':
a.cc:163:16: error: return-statement with a value, in function returning 'void' [-fpermissive]
  163 |         return 0;
      |                ^