Problem:
Score : 600 points

Problem Statement

We have a grid with A horizontal rows and B vertical columns, with the squares painted white. On this grid, we will repeatedly apply the following operation:

Assume that the grid currently has a horizontal rows and b vertical columns. Choose "vertical" or "horizontal".

If we choose "vertical", insert one row at the top of the grid, resulting in an (a+1) \times b grid.

If we choose "horizontal", insert one column at the right end of the grid, resulting in an a \times (b+1) grid.

Then, paint one of the added squares black, and the other squares white.

Assume the grid eventually has C horizontal rows and D vertical columns. Find the number of ways in which the squares can be painted in the end, modulo 998244353.

Constraints

1 \leq A \leq C \leq 3000

1 \leq B \leq D \leq 3000

A, B, C, and D are integers.

Input

Input is given from Standard Input in the following format:

A B C D

Output

Print the number of ways in which the squares can be painted in the end, modulo 998244353.

Sample Input 1

1 1 2 2

Sample Output 1

3

Any two of the three squares other than the bottom-left square can be painted black.

Sample Input 2

2 1 3 4

Sample Output 2

65

Sample Input 3

31 41 59 265

Sample Output 3

387222020

Solution in C# (.NET Core 3.1.201) (judge verdict: Accepted)

using System;
using System.Collections;
using System.Collections.Generic;
using System.Diagnostics;
using System.Diagnostics.CodeAnalysis;
using System.IO;
using System.Linq;
using System.Numerics;
using System.Reflection.Metadata.Ecma335;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
using System.Text;
using System.Threading;

namespace AtCoder
{
	public class Program
	{
		static void Main()
		{
			var cin = new Scanner();
			int a = cin.Int();
			int b = cin.Int();
			int c = cin.Int();
			int d = cin.Int();

			long P = 998244353;
			ModInt.P = 998244353;

			if (c < a || d < b) {
				Console.WriteLine(0);
				return;
			}

			int n = (c - a) + (d - b);
			int m = c - a;
			int l = d - b;

			//0:0 1:R1 2:R2 3:B1 4:B2 5:B1R1 6:R1B2 7:R2B1
			var dp = new long[n + 1, m + 1, 8];
			var done = new bool[n + 1, m + 1];
			dp[0, 0, 0] = 1;
			done[0, 0] = true;
			for (int i = 0; i < n; i++) {
				for (int j = 0; j < m + 1; j++) {
					if (done[i, j] == false) {
						continue;
					}

					int w = b + i - j;
					int h = a + j;
					if (j + 1 <= m) {
						//tate
						if (done[i + 1, j + 1] == false) {
							dp[i + 1, j + 1, 3] += (((dp[i, j, 0] + dp[i, j, 3]) % P) * (w - 1)) % P;
							dp[i + 1, j + 1, 3] %= P;
							dp[i + 1, j + 1, 5] += (dp[i, j, 0] + dp[i, j, 3]) % P;
							dp[i + 1, j + 1, 5] %= P;
							dp[i + 1, j + 1, 5]
								+= ((((dp[i, j, 1] + dp[i, j, 5]) % P + dp[i, j, 6]) % P) * (w - 1)) % P;
							dp[i + 1, j + 1, 5] %= P;
							dp[i + 1, j + 1, 7]
								+= ((dp[i, j, 1] + dp[i, j, 5]) % P + dp[i, j, 6]) % P;
							dp[i + 1, j + 1, 7] %= P;
							dp[i + 1, j + 1, 7]
								+= (((dp[i, j, 2] + dp[i, j, 7]) % P) * w) % P;
							dp[i + 1, j + 1, 7] %= P;
							done[i + 1, j + 1] = true;
						} else {
							dp[i + 1, j + 1, 7] += (((dp[i, j, 1] + dp[i, j, 5]) % P) + dp[i, j, 6]) % P;
							dp[i + 1, j + 1, 7] %= P;
							dp[i + 1, j + 1, 7] += ((dp[i, j, 2] + dp[i, j, 7]) % P * w) % P;
							dp[i + 1, j + 1, 7] %= P;
						}
					}

					if (w - b + 1 <= l) {
						//yoko
						if (done[i + 1, j] == false) {
							dp[i + 1, j, 1] += (((dp[i, j, 0] + dp[i, j, 1]) % P) * (h - 1)) % P;
							dp[i + 1, j, 1] %= P;
							dp[i + 1, j, 5] += (dp[i, j, 0] + dp[i, j, 1]) % P;
							dp[i + 1, j, 5] %= P;
							dp[i + 1, j, 5]
								+= ((((dp[i, j, 3] + dp[i, j, 5]) % P + dp[i, j, 7]) % P) * (h - 1)) % P;
							dp[i + 1, j, 5] %= P;
							dp[i + 1, j, 6]
								+= (((dp[i, j, 3] + dp[i, j, 5]) % P + dp[i, j, 7])) % P;
							dp[i + 1, j, 6] %= P;
							dp[i + 1, j, 6]
								+= (((dp[i, j, 4] + dp[i, j, 6]) % P) * h) % P;
							dp[i + 1, j, 6] %= P;
							done[i + 1, j] = true;
						} else {
							dp[i + 1, j, 6] += (((dp[i, j, 3] + dp[i, j, 5]) % P) + dp[i, j, 7]) % P;
							dp[i + 1, j, 6] %= P;
							dp[i + 1, j, 6] += (((dp[i, j, 4] + dp[i, j, 6]) % P) * h) % P;
							dp[i + 1, j, 6] %= P;
						}
					}
				}
			}

			ModInt ans = 0;
			for (int i = 0; i < 8; i++) {
				ans += dp[n, m, i];
			}

			Console.WriteLine(ans.Value);
		}
	}

	public struct ModInt
	{
		public static long P { get; set; } = (long)1e9 + 7;

		public static ModInt Pow(ModInt value, long k)
		{
			return Pow(value.Value, k);
		}

		public static ModInt Pow(long value, long k)
		{
			long ret = 1;
			for (k %= P - 1; k > 0; k >>= 1, value = value * value % P) {
				if ((k & 1) == 1) {
					ret = ret * value % P;
				}
			}
			return new ModInt(ret);
		}

		public static ModInt Inverse(ModInt value)
		{
			return Pow(value, P - 2);
		}

		public long Value;

		public ModInt(long value)
		{
			value %= P;
			if (value < 0) {
				value += P;
			}

			Value = value;
		}

		public static ModInt operator +(ModInt lhs, ModInt rhs)
		{
			lhs.Value += rhs.Value;
			if (lhs.Value >= P) {
				lhs.Value -= P;
			}
			return lhs;
		}

		public static ModInt operator -(ModInt lhs, ModInt rhs)
		{
			lhs.Value -= rhs.Value;
			if (lhs.Value < 0) {
				lhs.Value += P;
			}

			return lhs;
		}

		public static ModInt operator *(ModInt lhs, ModInt rhs)
		{
			return new ModInt(lhs.Value * rhs.Value % P);
		}
		public static ModInt operator /(ModInt lhs, ModInt rhs)
		{
			long exp = P - 2;
			while (exp > 0) {
				if (exp % 2 > 0) {
					lhs *= rhs;
				}

				rhs *= rhs;
				exp /= 2;
			}

			return lhs;
		}

		public static implicit operator ModInt(long n)
		{
			n %= P;
			if (n < 0) {
				n += P;
			}

			return new ModInt(n);
		}

		public override string ToString()
		{
			return Value.ToString();
		}
	}

	public class HashMap<TKey, TValue> : Dictionary<TKey, TValue>
	{
		private readonly Func<TKey, TValue> initialzier_;
		public HashMap(Func<TKey, TValue> initialzier)
			: base()
		{
			initialzier_ = initialzier;
		}

		public HashMap(Func<TKey, TValue> initialzier, int capacity)
			: base(capacity)
		{
			initialzier_ = initialzier;
		}

		new public TValue this[TKey key]
		{
			get
			{
				if (ContainsKey(key) == false) {
					base[key] = initialzier_(key);
				}

				return base[key];
			}

			set { base[key] = value; }
		}
	}

	public static class Helper
	{
		public static void UpdateMin<T>(ref T target, T value) where T : IComparable<T>
			=> target = target.CompareTo(value) > 0 ? value : target;

		public static void UpdateMin<T>(ref T target, T value, Action<T> onUpdated) where T : IComparable<T>
		{
			if (target.CompareTo(value) > 0) {
				target = value;
				onUpdated(value);
			}
		}

		public static void UpdateMax<T>(ref T target, T value) where T : IComparable<T>
			=> target = target.CompareTo(value) < 0 ? value : target;
		public static void UpdateMax<T>(ref T target, T value, Action<T> onUpdated) where T : IComparable<T>
		{
			if (target.CompareTo(value) < 0) {
				target = value;
				onUpdated(value);
			}
		}

		public static T[] Array<T>(int n, Func<int, T> init)
			=> Enumerable.Range(0, n).Select(x => init(x)).ToArray();
		public static List<T> List<T>(int n, Func<int, T> init)
			=> Enumerable.Range(0, n).Select(x => init(x)).ToList();
		public static T[,] Array2<T>(int n, int m, T init)
		{
			var array = new T[n, m];
			for (int i = 0; i < n; i++) {
				for (int j = 0; j < m; j++) {
					array[i, j] = init;
				}
			}

			return array;
		}

		public static T[,] Array2<T>(int n, int m, Func<int, int, T> initializer)
		{
			var array = new T[n, m];
			for (int i = 0; i < n; i++) {
				for (int j = 0; j < m; j++) {
					array[i, j] = initializer(i, j);
				}
			}

			return array;
		}

		public static T[,,] Array3<T>(int n1, int n2, int n3, T init)
		{
			var array = new T[n1, n2, n3];
			for (int i1 = 0; i1 < n1; i1++) {
				for (int i2 = 0; i2 < n2; i2++) {
					for (int i3 = 0; i3 < n3; i3++) {
						array[i1, i2, i3] = init;
					}
				}
			}

			return array;
		}

		private static readonly int[] delta4_ = { 1, 0, -1, 0, 1 };
		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public static void DoAt4(int i, int j, int imax, int jmax, Action<int, int> action)
		{
			for (int dn = 0; dn < 4; dn++) {
				int d4i = i + delta4_[dn];
				int d4j = j + delta4_[dn + 1];
				if ((uint)d4i < (uint)imax && (uint)d4j < (uint)jmax) {
					action(d4i, d4j);
				}
			}
		}

		private static readonly int[] delta8_ = { 1, 0, -1, 0, 1, 1, -1, -1, 1 };
		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public static void DoAt8(int i, int j, int imax, int jmax, Action<int, int> action)
		{
			for (int dn = 0; dn < 8; dn++) {
				int d8i = i + delta8_[dn];
				int d8j = j + delta8_[dn + 1];
				if ((uint)d8i < (uint)imax && (uint)d8j < (uint)jmax) {
					action(d8i, d8j);
				}
			}
		}
	}

	public class Scanner
	{
		private readonly char[] delimiter_ = new char[] { ' ' };
		private readonly string filePath_;
		private readonly Func<string> reader_;
		private string[] buf_;
		private int index_;

		public Scanner(string file = "")
		{
			if (string.IsNullOrWhiteSpace(file)) {
				reader_ = Console.ReadLine;
			} else {
				filePath_ = file;
				var fs = new StreamReader(file);
				reader_ = fs.ReadLine;
			}
			buf_ = new string[0];
			index_ = 0;
		}

		public string NextLine() => reader_();
		public string Next()
		{
			if (index_ < buf_.Length) {
				return buf_[index_++];
			}

			string st = reader_();
			while (st == "") {
				st = reader_();
			}

			buf_ = st.Split(delimiter_, StringSplitOptions.RemoveEmptyEntries);
			if (buf_.Length == 0) {
				return Next();
			}

			index_ = 0;
			return buf_[index_++];
		}

		public int Int() => int.Parse(Next());
		public long Long() => long.Parse(Next());
		public double Double() => double.Parse(Next());

		public int[] ArrayInt(int N, int add = 0)
		{
			int[] Array = new int[N];
			for (int i = 0; i < N; i++) {
				Array[i] = Int() + add;
			}
			return Array;
		}

		public long[] ArrayLong(int N, long add = 0)
		{
			long[] Array = new long[N];
			for (int i = 0; i < N; i++) {
				Array[i] = Long() + add;
			}
			return Array;
		}

		public double[] ArrayDouble(int N, double add = 0)
		{
			double[] Array = new double[N];
			for (int i = 0; i < N; i++) {
				Array[i] = Double() + add;
			}
			return Array;
		}

		public void Save(string text)
		{
			if (string.IsNullOrWhiteSpace(filePath_)) {
				return;
			}

			File.WriteAllText(filePath_ + "_output.txt", text);
		}
	}
}