poj3669 Meteor Shower(BFS)
我只想说这题WA了后去看讨论才发现的坑点，除了要注意原点外，流星范围题目给的是[0,300]，到302的位置就绝对安全了。。。
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 }
