bnuoj 25662 A Famous Grid (构图+BFS)

http://www.bnuoj.com/bnuoj/problem_show.php?pid=25662
  1 #include <iostream>
  2 #include <stdio.h>
  3 #include <string.h>
  4 #include <math.h>
  5 #include <algorithm>
  6 #include <stack>
  7 #include <queue>
  8 
  9 #define N 150
 10 using namespace std;
 11 
 12 struct Nod
 13 {
 14     int x,y,step;
 15 }node[15000];
 16 
 17 int map[N][N];
 18 int mark[N][N];
 19 int prim[15000];
 20 
 21 int cx[]={1,0,-1,0};
 22 int cy[]={0,1,0,-1};
 23 
 24 int cnt=1;
 25 
 26 void getMap(int x,int y,int re)
 27 {
 28     while(1)
 29     {
 30         int dx,dy;
 31         dx = x + cx[(re+1)%4];
 32         dy = y + cy[(re+1)%4];
 33         if(!(dx>=0&&dx<N&&dy>=0&&dy<N))
 34         {
 35             break;
 36         }
 37         if(map[dx][dy]==0)
 38         {
 39             map[dx][dy]= ++cnt;
 40             node[cnt].x = dx;
 41             node[cnt].y = dy;
 42           //  getMap(dx,dy,(re+1)%4);
 43             x = dx;
 44             y = dy;
 45             re = (re+1)%4;
 46         }
 47         else
 48         {
 49             dx = x + cx[re%4];
 50             dy = y + cy[re%4];
 51             if(!(dx>=0&&dx<N&&dy>=0&&dy<N))
 52             {
 53                 break ;
 54             }
 55             map[dx][dy]= ++cnt;
 56             node[cnt].x = dx;
 57             node[cnt].y = dy;
 58            // getMap(dx,dy,re);
 59             x = dx;
 60             y = dy;
 61         }
 62     }
 63 }
 64 
 65 int bfs(int x,int y)
 66 {
 67     memset(mark,0,sizeof(mark));
 68     queue<Nod> Q;
 69     Nod temp;
 70     temp.x = node[x].x;
 71     temp.y = node[x].y;
 72     temp.step = 0;
 73     Q.push(temp);
 74     mark[temp.x][temp.y] = 1;
 75     while(!Q.empty())
 76     {
 77         Nod td = Q.front();
 78         Q.pop();
 79         if(td.x==node[y].x&&td.y==node[y].y)
 80         {
 81             return td.step;
 82         }
 83         int i;
 84         for(i=0;i<4;i++)
 85         {
 86             temp.x = td.x + cx[i];
 87             temp.y = td.y + cy[i];
 88             temp.step = td.step + 1;
 89             if(map[temp.x][temp.y]>=1&&map[temp.x][temp.y]<=14000&&prim[map[temp.x][temp.y]]&&!mark[temp.x][temp.y])
 90             {
 91                 mark[temp.x][temp.y]=1;
 92                 Q.push(temp);
 93             }
 94         }
 95     }
 96     return -1;
 97 }
 98 
 99 
100 int main()
101 {
102     cnt=1;
103     int cas=1;
104     map[60][60]=1;
105     getMap(60,60,0);
106     node[1].x = 60;
107     node[1].y = 60;
108    // cout<<cnt<<endl;
109     int i,j;
110     prim[1]=1;
111     for(i=2;i<15000;i++)
112     {
113         for(j=2;j*j<=i;j++)
114         {
115             if(i%j==0)
116             {
117                 prim[i]=1;
118                 break;
119             }
120         }
121     }
122  //   for(i=1;i<=100;i++)
123    // if(!prim[i])cout<<i<<" ";
124 
125     int x,y;
126     while(~scanf("%d%d",&x,&y))
127     {
128         printf("Case %d: ",cas++);
129         int ans = bfs(x,y);
130         if(ans==-1)
131         {
132             puts("impossible");
133         }
134         else
135         {
136             printf("%d
",ans);
137         }
138     }
139 
140     return 0;
141 }