uva 10047 the monocyle (四维bfs)

算法指南白书

维护一个四维数组，走一步更新一步

 #include<cstdio>
 #include<cstring>
 #include<queue>
 #include<algorithm>
 using namespace std;

 const int INF = ;
 const int maxr =  + ;
 const int maxc =  + ;
 int R, C, sr, sc, tr, tc;
 char maze[maxr][maxc];

 struct State {
     int r, c, dir, color;
     State(int r, int c, int dir, int color):r(r),c(c),dir(dir),color(color) {}
 };

 const int dr[] = {-,,,}; // north, west, south, east
 const int dc[] = {,-,,};
 int d[maxr][maxc][][], vis[maxr][maxc][][];//横坐标,纵坐标,方向,颜色

 int ans;
 queue<State> Q;

 void update(int r, int c, int dir, int color, int v) {
     if(r <  || r >= R || c <  || c >= C) return; // 不能走出边界
     if(maze[r][c] == '.' && !vis[r][c][dir][color]) {
         Q.push(State(r, c, dir, color));
         vis[r][c][dir][color] = ;
         d[r][c][dir][color] = v;
         if(r == tr && c == tc && color == ) ans = min(ans, v); // 更新答案
     }
 }

 void bfs(State st) {
     d[st.r][st.c][st.dir][st.color] = ;
     vis[st.r][st.c][st.dir][st.color] = ;
     Q.push(st);
     while(!Q.empty()) {
         st = Q.front();
         Q.pop();
         int v = d[st.r][st.c][st.dir][st.color] + ;
         update(st.r, st.c, (st.dir+)%, st.color, v); // 左转
         update(st.r, st.c, (st.dir+)%, st.color, v); // 右转
         update(st.r+dr[st.dir], st.c+dc[st.dir], st.dir, (st.color+)%, v); // 前进
     }
 }

 int main() {
     int kase = ;
     while(scanf("%d%d", &R, &C) ==  && R && C) {
         for(int i = ; i < R; i++) {
             scanf("%s", maze[i]);
             for(int j = ; j < C; j++)
                 if(maze[i][j] == 'S') {
                     sr = i;
                     sc = j;
                 } else if(maze[i][j] == 'T') {
                     tr = i;
                     tc = j;
                 }
         }
         maze[sr][sc] = maze[tr][tc] = '.';
         ans = INF;
         memset(vis, , sizeof(vis));
         bfs(State(sr, sc, , ));

         if(kase > ) printf("\n");
         printf("Case #%d\n", ++kase);
         if(ans == INF) printf("destination not reachable\n");
         else printf("minimum time = %d sec\n", ans);
     }
 }