【HDOJ】3085 Nightmare Ⅱ

双向BFS。注意，任何一个点出队后，首先需要考虑ghost。

  1 /* 3085 */
  2 #include <iostream>
  3 #include <queue>
  4 #include <cstdio>
  5 #include <cstring>
  6 #include <cstdlib>
  7 #include <cmath>
  8 using namespace std;
  9
 10 #define MAXN 805
 11
 12 typedef struct node_t {
 13     int x, y;
 14     node_t() {}
 15     node_t(int xx, int yy) {
 16         x = xx; y = yy;
 17     }
 18 } node_t;
 19
 20 int n, m;
 21 node_t z[2], beg0, beg1;
 22 char map[MAXN][MAXN];
 23 bool visit0[MAXN][MAXN];
 24 bool visit1[MAXN][MAXN];
 25 int dir[4][2] = {
 26     -1,0,1,0,0,-1,0,1
 27 };
 28
 29 inline bool check(int x, int y) {
 30     return x<0 || x>=n || y<0 || y>=m;
 31 }
 32
 33 inline bool meetZ(int x, int y, int t) {
 34     return abs(x-z[0].x)+abs(y-z[0].y)<=t+t || abs(x-z[1].x)+abs(y-z[1].y)<=t+t;
 35 }
 36
 37 int bfs() {
 38     int size;
 39     int x, y, t = 0;
 40     int i, j, k, r;
 41     node_t nd;
 42     queue<node_t> Q0;
 43     queue<node_t> Q1;
 44
 45     memset(visit0, false, sizeof(visit0));
 46     memset(visit1, false, sizeof(visit1));
 47     visit0[beg0.x][beg0.y] = true;
 48     visit1[beg1.x][beg1.y] = true;
 49     Q0.push(beg0);
 50     Q1.push(beg1);
 51
 52     while (!Q0.empty() || !Q1.empty()) {
 53         ++t;
 54         // Q0
 55         r = 3;
 56         while (r--) {
 57             size = Q0.size();
 58             while (size--) {
 59                 nd = Q0.front();
 60                 Q0.pop();
 61                 if (meetZ(nd.x, nd.y, t))
 62                     continue;
 63                 for (i=0; i<4; ++i) {
 64                     x = nd.x + dir[i][0];
 65                     y = nd.y + dir[i][1];
 66                     if (check(x, y) || visit0[x][y])
 67                         continue;
 68                     if (map[x][y]==‘X‘ || meetZ(x, y, t))
 69                         continue;
 70                     if (visit1[x][y])
 71                         return t;
 72                     visit0[x][y] = true;
 73                     Q0.push(node_t(x, y));
 74                 }
 75             }
 76         }
 77         // Q1
 78         size = Q1.size();
 79         while (size--) {
 80             nd = Q1.front();
 81             Q1.pop();
 82             if (meetZ(nd.x, nd.y, t))
 83                 continue;
 84             for (i=0; i<4; ++i) {
 85                 x = nd.x + dir[i][0];
 86                 y = nd.y + dir[i][1];
 87                 if (check(x, y) || visit1[x][y])
 88                     continue;
 89                 if (map[x][y]==‘X‘ || meetZ(x, y, t))
 90                     continue;
 91                 if (visit0[x][y])
 92                     return t;
 93                 visit1[x][y] = true;
 94                 Q1.push(node_t(x, y));
 95             }
 96         }
 97     }
 98
 99     return -1;
100 }
101
102 int main() {
103     int t;
104     int i, j, k;
105
106     #ifndef ONLINE_JUDGE
107         freopen("data.in", "r", stdin);
108         freopen("data.out", "w", stdout);
109     #endif
110
111     scanf("%d", &t);
112     while (t--) {
113         scanf("%d %d", &n, &m);
114         k = 0;
115         for (i=0; i<n; ++i) {
116             scanf("%s", map[i]);
117             for (j=0; j<m; ++j) {
118                 if (map[i][j] == ‘Z‘) {
119                     z[k].x = i;
120                     z[k].y = j;
121                     ++k;
122                 } else if (map[i][j] == ‘M‘) {
123                     beg0.x = i;
124                     beg0.y = j;
125                 } else if (map[i][j] == ‘G‘) {
126                     beg1.x = i;
127                     beg1.y = j;
128                 }
129             }
130         }
131         k = bfs();
132         printf("%d\n", k);
133     }
134
135     return 0;
136 }