Problem:
Score : 500 points

Problem Statement

We have a deck consisting of N cards. Each card has an integer written on it. The integer on the i-th card from the top is a_i.

Two people X and Y will play a game using this deck. Initially, X has a card with Z written on it in his hand, and Y has a card with W written on it in his hand. Then, starting from X, they will alternately perform the following action:

Draw some number of cards from the top of the deck. Then, discard the card in his hand and keep the last drawn card instead. Here, at least one card must be drawn.

The game ends when there is no more card in the deck. The score of the game is the absolute difference of the integers written on the cards in the two players' hand.

X will play the game so that the score will be maximized, and Y will play the game so that the score will be minimized. What will be the score of the game?

Constraints

All input values are integers.

1 \leq N \leq 2000

1 \leq Z, W, a_i \leq 10^9

Input

Input is given from Standard Input in the following format:

N Z W
a_1 a_2 ... a_N

Output

Print the score.

Sample Input 1

3 100 100
10 1000 100

Sample Output 1

900

If X draws two cards first, Y will draw the last card, and the score will be |1000 - 100| = 900.

Sample Input 2

3 100 1000
10 100 100

Sample Output 2

900

If X draws all the cards first, the score will be |1000 - 100| = 900.

Sample Input 3

5 1 1
1 1 1 1 1

Sample Output 3

0

Sample Input 4

1 1 1
1000000000

Sample Output 4

999999999

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

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;

public static class Ex
{
    public static bool IsNullOrEmpty(this string s) { return string.IsNullOrEmpty(s); }
    public static List<string> FastSort(this List<string> s) { s.Sort(StringComparer.OrdinalIgnoreCase); return s.ToList(); }
    public static void yesno(this bool b) { Console.WriteLine(b ? "yes" : "no"); }
    public static void YesNo(this bool b) { Console.WriteLine(b ? "Yes" : "No"); }
    public static void YESNO(this bool b) { Console.WriteLine(b ? "YES" : "NO"); }
    public static int PopCount(this int bits)
    {
        bits = (bits & 0x55555555) + (bits >> 1 & 0x55555555);
        bits = (bits & 0x33333333) + (bits >> 2 & 0x33333333);
        bits = (bits & 0x0f0f0f0f) + (bits >> 4 & 0x0f0f0f0f);
        bits = (bits & 0x00ff00ff) + (bits >> 8 & 0x00ff00ff);
        return (bits & 0x0000ffff) + (bits >> 16 & 0x0000ffff);
    }
}



partial class Program
{
    public string GetStr() { return Console.ReadLine().Trim(); }
    public char GetChar() { return Console.ReadLine().Trim()[0]; }
    public int GetInt() { return int.Parse(Console.ReadLine().Trim()); }
    public long GetLong() { return long.Parse(Console.ReadLine().Trim()); }
    public double GetDouble() { return double.Parse(Console.ReadLine().Trim()); }
    public string[] GetStrArray() { return Console.ReadLine().Trim().Split(' '); }
    public string[][] GetStrArray(int N)
    {
        var res = new string[N][];
        for (int i = 0; i < N; i++) res[i] = Console.ReadLine().Trim().Split(' ');
        return res;
    }
    public int[] GetIntArray() { return Console.ReadLine().Trim().Split(' ').Select(int.Parse).ToArray(); }
    public int[][] GetIntArray(int N)
    {
        var res = new int[N][];
        for (int i = 0; i < N; i++) res[i] = Console.ReadLine().Trim().Split(' ').Select(int.Parse).ToArray();
        return res;
    }
    public long[] GetLongArray() { return Console.ReadLine().Trim().Split(' ').Select(long.Parse).ToArray(); }
    public long[][] GetLongArray(int N)
    {
        var res = new long[N][];
        for (int i = 0; i < N; i++) res[i] = Console.ReadLine().Trim().Split(' ').Select(long.Parse).ToArray();
        return res;
    }
    public char[] GetCharArray() { return Console.ReadLine().Trim().Split(' ').Select(char.Parse).ToArray(); }
    public double[] GetDoubleArray() { return Console.ReadLine().Trim().Split(' ').Select(double.Parse).ToArray(); }
    public double[][] GetDoubleArray(int N)
    {
        var res = new double[N][];
        for (int i = 0; i < N; i++) res[i] = Console.ReadLine().Trim().Split(' ').Select(double.Parse).ToArray();
        return res;
    }
    public char[][] GetGrid(int H)
    {
        var res = new char[H][];
        for (int i = 0; i < H; i++) res[i] = Console.ReadLine().Trim().ToCharArray();
        return res;
    }
    public T[] CreateArray<T>(int N, T value)
    {
        var res = new T[N];
        for (int i = 0; i < N; i++) res[i] = value;
        return res;
    }
    public T[][] CreateArray<T>(int H, int W, T value)
    {
        var res = new T[H][];
        for (int i = 0; i < H; i++)
        {
            res[i] = new T[W];
            for (int j = 0; j < W; j++) res[i][j] = value;
        }
        return res;
    }
    public T[][][] CreateArray<T>(int H, int W, int R, T value)
    {
        var res = new T[H][][];
        for (int i = 0; i < H; i++)
        {
            res[i] = new T[W][];
            for (int j = 0; j < W; j++)
            {
                res[i][j] = new T[R];
                for (int k = 0; k < R; k++) res[i][j][k] = value;
            }
        }
        return res;
    }

    Dictionary<int, List<int>> GetUnweightedAdjacencyList(int N, int M, bool isDirected, bool isNode_0indexed)
    {
        var dic = new Dictionary<int, List<int>>();
        foreach (var e in Enumerable.Range(0, N)) { dic.Add(e, new List<int>()); }
        for (int i = 0; i < M; i++)
        {
            var input = GetIntArray();
            var a = isNode_0indexed ? input[0] : input[0] - 1;
            var b = isNode_0indexed ? input[1] : input[1] - 1;
            dic[a].Add(b);
            if (isDirected == false) dic[b].Add(a);
        }
        return dic;
    }
    Dictionary<int, List<Edge>> GetWeightedAdjacencyList(int N, int M, bool isDirected, bool isNode_0indexed)
    {
        var dic = new Dictionary<int, List<Edge>>();
        foreach (var e in Enumerable.Range(0, N)) { dic.Add(e, new List<Edge>()); }
        for (int i = 0; i < M; i++)
        {
            var input = GetIntArray();
            var a = isNode_0indexed ? input[0] : input[0] - 1;
            var b = isNode_0indexed ? input[1] : input[1] - 1;
            var c = input[2];
            dic[a].Add(new Edge(b, c));
            if (isDirected == false) dic[b].Add(new Edge(a, c));
        }
        return dic;
    }

    bool eq<T, U>() => typeof(T).Equals(typeof(U));
    T ct<T, U>(U a) => (T)Convert.ChangeType(a, typeof(T));
    T cv<T>(string s) => eq<T, int>() ? ct<T, int>(int.Parse(s))
                       : eq<T, long>() ? ct<T, long>(long.Parse(s))
                       : eq<T, double>() ? ct<T, double>(double.Parse(s))
                       : eq<T, char>() ? ct<T, char>(s[0])
                                         : ct<T, string>(s);
    void Multi<T>(out T a) => a = cv<T>(GetStr());
    void Multi<T, U>(out T a, out U b)
    {
        var ar = GetStrArray(); a = cv<T>(ar[0]); b = cv<U>(ar[1]);
    }
    void Multi<T, U, V>(out T a, out U b, out V c)
    {
        var ar = GetStrArray(); a = cv<T>(ar[0]); b = cv<U>(ar[1]); c = cv<V>(ar[2]);
    }
    void Multi<T, U, V, W>(out T a, out U b, out V c, out W d)
    {
        var ar = GetStrArray(); a = cv<T>(ar[0]); b = cv<U>(ar[1]); c = cv<V>(ar[2]); d = cv<W>(ar[3]);
    }
    void Multi<T, U, V, W, X>(out T a, out U b, out V c, out W d, out X e)
    {
        var ar = GetStrArray(); a = cv<T>(ar[0]); b = cv<U>(ar[1]); c = cv<V>(ar[2]); d = cv<W>(ar[3]); e = cv<X>(ar[4]);
    }
    void Multi<T, U, V, W, X, Y>(out T a, out U b, out V c, out W d, out X e, out Y f)
    {
        var ar = GetStrArray(); a = cv<T>(ar[0]); b = cv<U>(ar[1]); c = cv<V>(ar[2]); d = cv<W>(ar[3]); e = cv<X>(ar[4]); f = cv<Y>(ar[5]);
    }

    int[] dx = new int[] { 1, 0, -1, 0, 1, 1, -1, -1 };
    int[] dy = new int[] { 0, 1, 0, -1, 1, -1, 1, -1 };
}

class Pair : IComparable<Pair>
{
    public Pair(int node, long cost)
    {
        Node = node; Cost = cost;
    }
    public int Node { get; set; }
    public long Cost { get; set; }
    public int CompareTo(Pair p)
    {
        return p.Cost > Cost ? 1 : -1;
    }
}

class Edge
{
    public Edge(int to, long length)
    {
        To = to;
        Length = length;
    }
    public int To { get; set; }
    public long Length { get; set; }
}

class Comparable : IComparable<Comparable>
{
    public Comparable(int value)
    {
        Value = value;
    }

    public int Value { get; set; }
    public int CompareTo(Comparable c)
    {
        var a = Math.Abs(Value);
        var b = Math.Abs(c.Value);
        return a > b ? 1 : a == b ? 0 : -1;
    }
}

class Comparer<T> : IComparer<T>
{
    public int Compare(T t1, T t2)
    {
        return 1;
    }
}

partial class Program
{
    static void Main()
    {
        Console.SetOut(new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false });
        new Program().Solve();
        Console.Out.Flush();
        Console.Read();
    }

    public void Solve()
    {
        int N, Z, W;
        Multi(out N, out Z, out W);
        var B = GetIntArray().Reverse().ToArray();
        var dp = CreateArray(N, 2, 0);
        for (int i = 1; i < N; i++)
        {
            int xmax = 0;
            int ymin = int.MaxValue;
            for (int j = 1; j < i; j++)
            {
                xmax = Math.Max(xmax, dp[j][1]);
                ymin = Math.Min(ymin, dp[j][0]);
            }
            dp[i][0] = Math.Max(xmax, Math.Abs(B[0] - B[i]));
            dp[i][1] = Math.Min(ymin, Math.Abs(B[0] - B[i]));

        }
        var max = 0;
        for (int i = 1; i < N; i++)
        {
            max = Math.Max(max, dp[i][1]);
        }
        Console.WriteLine(Math.Max(max, Math.Abs(B[0] - W)));
    }
}