【题目链接】
http://poj.org/problem?id=3322
【算法】
广度优先搜索
【代码】
#include <algorithm> #include <bitset> #include <cctype> #include <cerrno> #include <clocale> #include <cmath> #include <complex> #include <cstdio> #include <cstdlib> #include <cstring> #include <ctime> #include <deque> #include <exception> #include <fstream> #include <functional> #include <limits> #include <list> #include <map> #include <iomanip> #include <ios> #include <iosfwd> #include <iostream> #include <istream> #include <ostream> #include <queue> #include <set> #include <sstream> #include <stdexcept> #include <streambuf> #include <string> #include <utility> #include <vector> #include <cwchar> #include <cwctype> #include <stack> #include <limits.h> using namespace std; #define MAXN 510 int i,j,n,m; char mp[MAXN][MAXN]; const int dx[4] = {0,0,-1,1}; const int dy[4] = {-1,1,0,0}; const int nx[3][4] = {{0,0,-2,1},{0,0,-1,1},{0,0,-1,2}}; const int ny[3][4] = {{-2,1,0,0},{-1,2,0,0},{-1,1,0,0}}; const int nxt[3][4] = {{1,1,2,2},{0,0,1,1},{2,2,0,0}}; struct info { int x,y; int state; }; inline bool ok(int x,int y) { return x >= 1 && x <= n && y >= 1 && y <= m; } inline bool check(int x,int y,int state) { if (!ok(x,y)) return false; if (state == 0 && (mp[x][y] == '#' || mp[x][y] == 'E')) return false; if (state == 1 && (!ok(x,y+1) || mp[x][y] == '#' || mp[x][y+1] == '#')) return false; if (state == 2 && (!ok(x+1,y) || mp[x][y] == '#' || mp[x+1][y] == '#')) return false; return true; } inline void bfs() { int i,j,k,tx,ty,ts; info s,e,cur; queue< info > q; static int dist[MAXN][MAXN][3]; while (!q.empty()) q.pop(); for (i = 1; i <= n; i++) { for (j = 1; j <= m; j++) { for (k = 0; k < 3; k++) { dist[i][j][k] = -1; } } } for (i = 1; i <= n; i++) { for (j = 1; j <= m; j++) { if (mp[i][j] == 'X') { s.x = i; s.y = j; s.state = 0; for (k = 0; k < 4; k++) { tx = i + dx[k]; ty = j + dy[k]; if (ok(tx,ty) && mp[tx][ty] == 'X') { s.x = min(i,tx); s.y = min(j,ty); if (k < 2) s.state = 1; else s.state = 2; } } } if (mp[i][j] == 'O') { e.x = i; e.y = j; e.state = 0; } } } dist[s.x][s.y][s.state] = 0; q.push(s); while (!q.empty()) { cur = q.front(); q.pop(); for (i = 0; i < 4; i++) { tx = cur.x + nx[cur.state][i]; ty = cur.y + ny[cur.state][i]; ts = nxt[cur.state][i]; if (check(tx,ty,ts) && dist[tx][ty][ts] == -1) { q.push((info){tx,ty,ts}); dist[tx][ty][ts] = dist[cur.x][cur.y][cur.state] + 1; if (tx == e.x && ty == e.y && ts == e.state) { printf("%d\n",dist[tx][ty][ts]); return; } } } } printf("Impossible\n"); } int main() { while (scanf("%d%d",&n,&m) && n && m) { getchar(); for (i = 1; i <= n; i++) { for (j = 1; j <= m; j++) { mp[i][j] = getchar(); } getchar(); } bfs(); } return 0; }