题目：Link

代码：

#include <iostream>
#include <cstring>
#include <queue>
using namespace std;

struct rec {
    int x, y, lie;
};

#define maxn 505
#define int long long 
#define _for(i, a, b) for (int i = (a); i <= (b); i++)
const int dx[] = { 0,0,-1,1 };
const int dy[] = { -1,1,0,0 };
const int next_x[3][4] = { { 0,0,-2,1 }, 
                           { 0,0,-1,1 }, 
                           { 0,0,-1,2 } };
const int next_y[3][4] = { { -2,1,0,0 }, 
                           { -1,2,0,0 }, 
                           { -1,1,0,0 } };
const int next_lie[3][4] = { { 1,1,2,2 }, 
                             { 0,0,1,1 }, 
                             { 2,2,0,0 } };

int n, m;
int vis[maxn][maxn][3], ans[maxn][maxn][3];
char s[maxn][maxn];
queue<rec> q;
rec st, ed;

char read() {
    char ch = getchar();
    while(ch != 'O' && ch != 'X' && ch != '.' && ch != 'E' && ch != '#')
        ch = getchar();
    return ch;
}

bool valid1(int x, int y) {
    if (x < 0 || y < 0 || x >= n || y >= m)
        return false;
    return true;
}

bool valid2(rec l) {
    if (!valid1(l.x, l.y)) return false;
    if (l.lie == 0 && (s[l.x][l.y] == '#' || s[l.x][l.y] == 'E')) return false;
    if (l.lie == 1 && (s[l.x][l.y] == '#' || s[l.x][l.y + 1] == '#')) return false;
    if (l.lie == 2 && (s[l.x][l.y] == '#' || s[l.x + 1][l.y] == '#')) return false;
    return true;
}

void parse_st_ed() {
    _for (i, 0, n)
        _for (j, 0, m)
            if (s[i][j] == 'O')
                ed.x = i, ed.y = j, ed.lie = 0, s[i][j] = '.';
    _for (i, 0, n)
        _for (j, 0, m) {
            if (s[i][j] == 'X') {
                _for (k, 0, 3) {
                    int x = i + dx[k], y = j + dy[i];
                    if (valid1(x, y) && s[x][y] == 'X') {
                        st.x = min(x, i), st.y = min(y, j), st.lie = (k > 2) ? 2 : 1; 
                        s[i][j] = s[x][y] = '.';
                    }
                }
                if (s[i][j] == 'X')
                    st.x = i, st.y = j, st.lie = 0, s[i][j] = '.';
            }
        }
}

void bfs() {
    memset(vis, 0, sizeof(vis));
    ans[st.x][st.y][st.lie] = 0;
    q.push(st);
    while(!q.empty()) {
        rec l = q.front(); q.pop();
        if (l.x == ed.x && l.y == ed.y && l.lie == ed.lie) {cout << ans[l.x][l.y][l.lie] << endl; return;}           
        _for (i, 0, 3) {
            int x = l.x + next_x[l.lie][i];
            int y = l.y + next_y[l.lie][i];
            int lie = next_lie[l.lie][i];
            rec u;
            u.x = x, u.y = y, u.lie = lie;
            if (!valid2(u) || vis[x][y][lie])
                continue;
            vis[x][y][lie] = true;
            ans[x][y][lie] = ans[l.x][l.y][l.lie] + 1;
        }
    }
    cout << "Impossible" << endl;
}

signed main() {
    cin >> n >> m;
    while (n != 0 && m != 0) {
        while (!q.empty()) q.pop();
        memset(ans, -1, sizeof(ans));
        _for (i, 1, n)  _for (j, 1, m)  s[i][j] = read();
        parse_st_ed();
        bfs();
        cin >> n >> m;
    }
    return 0;
}