poj3669 Meteor Shower(BFS)

 1 #include<cstdio>
 2 #include<cmath>
 3 #include<queue>
 4 #include<cstring>
 5 #include<algorithm>
 6 #define CLR(a,b) memset((a),(b),sizeof((a)))
 7 using namespace std;
 8 
 9 const int N = 303;
10 const int inf = 0x3f3f3f3f;
11 int dir[][2]={-1,0,1,0,0,1,0,-1};
12 int vis[N][N], g[N][N];
13 struct point{
14     int x, y;
15     int d;
16     point(int x=0,int y=0,int d=0):x(x),y(y),d(d){}
17 };
18 int jud(int x, int y, int d){
19     if(x >=0 && x < N && y >= 0 && y < N && !vis[x][y] && d < g[x][y])
20         return 1;
21     return 0;
22 }
23 int bfs(){
24     CLR(vis, 0);
25     queue<point>q;
26     point u, v;
27     vis[0][0] = 0;
28     q.push(point(0,0,0));
29     while(!q.empty()){
30         u = q.front(); q.pop();
31         for(int i = 0; i < 4; ++i){
32             v.x = u.x + dir[i][0];
33             v.y = u.y + dir[i][1];
34             v.d = u.d + 1;
35             if(jud(v.x, v.y, v.d)){
36                 if(g[v.x][v.y] == inf)//安全区域
37                     return v.d;
38                 vis[v.x][v.y] = 1;
39                 q.push(v);
40             }
41         }
42     }
43     return -1;
44 }
45 int main(){
46     int m, i, x, y, t;
47     CLR(g,inf);
48     scanf("%d", &m);
49     for(i = 0; i < m; ++i){
50         scanf("%d%d%d", &x, &y, &t);
51         g[x][y] = min(t, g[x][y]);
52         if(x > 0 && t < g[x-1][y])
53             g[x-1][y] = t;
54         if(y > 0 && t < g[x][y-1])
55             g[x][y-1] = t;
56         g[x+1][y] = min(t, g[x+1][y]);
57         g[x][y+1] = min(t, g[x][y+1]);
58     }
59     if(g[0][0] == 0){printf("-1\n");return 0;}
60     if(g[0][0] == inf){printf("0\n");return 0;}
61     printf("%d\n",bfs());
62     return 0;
63 }