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++ (GCC 9.2.1) (judge verdict: Wrong Answer)

#include <bits/stdc++.h>
using namespace std;

#define CPP_STR(x) CPP_STR_I(x)
#define CPP_CAT(x,y) CPP_CAT_I(x,y)
#define CPP_STR_I(args...) #args
#define CPP_CAT_I(x,y) x ## y

using i8  = int8_t;
using u8  = uint8_t;
using i16 = int16_t;
using u16 = uint16_t;
using i32 = int32_t;
using u32 = uint32_t;
using i64 = int64_t;
using u64 = uint64_t;

using f32 = float;
using f64 = double;

#define FOR(i, start, end) for(i64 i = (start), CPP_CAT(i,xxxx_end)=(end); i < CPP_CAT(i,xxxx_end); ++i)
#define REP(i, n) FOR(i, 0, n)
#define REPS(i, n) for(i64 i = 1; i <= n; ++i)
#define RREP(i, n) for(i64 i = n - 1; i >= 0 ; --i)
#define RREPS(i, n) for(i64 i = n; i >= 1; --i)

#define ALL(f,c,...) (([&](decltype((c)) cccc) { return (f)(std::begin(cccc), std::end(cccc), ## __VA_ARGS__); })(c))

#define UNIQUE(v) v.erase( unique(v.begin(), v.end()), v.end() );

#define pb push_back
#define mp make_pair

template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; }

template<typename C>
i64 SIZE(const C& c) { return static_cast<i64>(c.size()); }

template<typename T, size_t N>
i64 SIZE(const T (&)[N]) { return static_cast<i64>(N); }

#define YES(n) cout << ((n) ? "YES" : "NO"  ) << endl
#define Yes(n) cout << ((n) ? "Yes" : "No"  ) << endl
#define POSSIBLE(n) cout << ((n) ? "POSSIBLE" : "IMPOSSIBLE"  ) << endl
#define Possible(n) cout << ((n) ? "Possible" : "Impossible"  ) << endl

#define VIN(x) for(auto&youso_: (x) )cin>>youso_
#define VOUT(x, delim) for(auto&youso_: (x) )cout<<youso_<<delim;cout<<endl

#define COUT(x) cout<<(x)<<endl
void CINT(){}
template <class Head,class... Tail>
void CINT(Head&& head,Tail&&... tail){
    cin>>head;
    CINT(move(tail)...);
}
#define CIN(...) i64 __VA_ARGS__;CINT(__VA_ARGS__)
#define SCIN(...) string __VA_ARGS__;CINT(__VA_ARGS__)


struct ProconInit {
    static constexpr int IOS_PREC = 15;
    static constexpr bool AUTOFLUSH = false;

    ProconInit() {
        cin.tie(nullptr);
        ios::sync_with_stdio(false);
        cout << fixed << setprecision(IOS_PREC);
        if(AUTOFLUSH)
            cout << unitbuf;
    }
} PROCON_INIT;

using P = pair<i64, i64>;

int main() {
    CIN(N, X, Y);
    vector<i64> A(N);
    VIN(A);

    if (N == 1) {
        cout << abs(A[0] - Y) << endl;
        return 0;
    }

    i64 maxv = abs(A[N - 1] - Y);
    set<P> candid;
    candid.emplace(Y, 0);
    RREP(i, A.size() + 1) {
        if (i == 0) continue;
        i64 x = A[i - 1];

        P y1, y2;
        auto it = candid.lower_bound({x, 0});
        if (it == candid.end()) {
            y1 = *(--it);
            y2 = {Y, 0};
        } else if (it == candid.begin()) {
            y1 = {Y, 0};
            y2 = *it;
        } else {
            y1 = *it;
            y2 = *(--it);
        }

        if (i > 0) candid.emplace(A[i - 1], i);

        if (y1.second != N && y2.second != N) continue;

        i64 d1 = abs(x - y1.first);
        i64 d2 = abs(x - y2.first);
        if (d1 < d2) {
            if (y1.second != N) continue;
            chmax(maxv, d1);
        } else if (d1 > d2) {
            if (y2.second != N) continue;
            chmax(maxv, d2);
        } else {
            chmax(maxv, d1);
        }
    }
    COUT(maxv);

    return 0;
}