Problem Description

　　Harry Potter has some precious. For example, his invisible robe, his wand and his owl. When Hogwarts school is in holiday, Harry Potter has to go back to uncle Vernon's home. But he can't bring his precious with him. As you know, uncle Vernon never allows
such magic things in his house. So Harry has to deposit his precious in the Gringotts Wizarding Bank which is owned by some goblins. The bank can be considered as a N × M grid consisting of N × M rooms. Each room has a coordinate. The coordinates of the upper-left
room is (1,1) , the down-right room is (N,M) and the room below the upper-left room is (2,1)..... A 3×4 bank grid is shown below:








　　Some rooms are indestructible and some rooms are vulnerable. Goblins always care more about their own safety than their customers' properties, so they live in the indestructible rooms and put customers' properties in vulnerable rooms. Harry Potter's precious
are also put in some vulnerable rooms. Dudely wants to steal Harry's things this holiday. He gets the most advanced drilling machine from his father, uncle Vernon, and drills into the bank. But he can only pass though the vulnerable rooms. He can't access
the indestructible rooms. He starts from a certain vulnerable room, and then moves in four directions: north, east, south and west. Dudely knows where Harry's precious are. He wants to collect all Harry's precious by as less steps as possible. Moving from
one room to another adjacent room is called a 'step'. Dudely doesn't want to get out of the bank before he collects all Harry's things. Dudely is stupid.He pay you $1,000,000 to figure out at least how many steps he must take to get all Harry's precious.

 

Input

　　There are several test cases.

　　In each test cases:

　　The first line are two integers N and M, meaning that the bank is a N × M grid(0<N,M <= 100).

　　Then a N×M matrix follows. Each element is a letter standing for a room. '#' means a indestructible room, '.' means a vulnerable room, and the only '@' means the vulnerable room from which Dudely starts to move.

　　The next line is an integer K ( 0 < K <= 4), indicating there are K Harry Potter's precious in the bank.

　　In next K lines, each line describes the position of a Harry Potter's precious by two integers X and Y, meaning that there is a precious in room (X,Y).

　　The input ends with N = 0 and M = 0

 

Output

　　For each test case, print the minimum number of steps Dudely must take. If Dudely can't get all Harry's things, print -1.

 

Sample Input

2 3

##@

#.#

1

2 2

4 4

#@##

....

####

....

2

2 1

2 4

0 0

 

Sample Output

-1

5

 

Source

2013 Asia Hangzhou Regional Contest

这题有些人用什么压缩dp写的，俺不会，后来发现一种超级巧妙的方法

你看啊k最多总共仅仅有4个点增加a1,a2,a3,a4，起点是a0，那么从a0一直遍历全部点不就是a0->a1->a2-》a3->a4的a1,a2,a3,a4的全排列吗，最多4！直接爆力，每次用next_permutaion（）更新排列就可以。当天假设k比較大这样的方法不行

还有注意next_permuation(a,a+n)假设你是从下标1開始的就是（a+1,a+n+1)不然会一直WA！

#include <iostream>

#include <cstring>

#include <queue>

#include <cstdio>

#include <algorithm>

using namespace std;

int n , m,k;

int visit[110][110];

int p[5];

char g[110][110];

int sx,sy;

int dx[] = {-1,1,0,0};

int dy[] = {0,0,-1,1};

struct node

{

    int x,y,step;

    node(int a,int b, int c): x(a),y(b),step(c) {}

    node(){}

}ss[6];

int  bfs()

{

    queue<node> q;

    q.push(node(sx,sy,0));

    memset(visit,0,sizeof(visit));

    visit[sx][sy] = 1;

    for(int i = 0; !q.empty(); )

    {

       node temp = q.front();

       q.pop();

       for(int j = 0; j < 4; j++)

       {

           int xx = temp.x + dx[j];

           int yy = temp.y + dy[j];

           int step = temp.step + 1;

           if(xx < 0 || yy < 0 || xx >= n || yy >= m || g[xx][yy] == '#' || visit[xx][yy]) continue;

           int flag = xx == ss[p[i]].x && yy == ss[p[i]].y;

           if(flag)

           {

               while(!q.empty()) q.pop();

               memset(visit,0,sizeof(visit));

               if(++i == k) return step;

           }

           q.push(node(xx,yy,step));

           visit[xx][yy] = 1;

           if(flag) break;

       }

    }

    return -1;

}

int main()

{

#ifdef xxz

    freopen("in.txt","r",stdin);

#endif

    while(scanf("%d%d",&n,&m)!=EOF && n != 0)

    {

        for(int i = 0; i < n; i++)

        {

              scanf("%s",g[i]);

              for(int j = 0; j < m; j++)

              {

                  if(g[i][j] == '@')

                  {

                    sx = i;

                    sy = j;

                  }

              }

        }

        scanf("%d",&k);

        int Case = 1;

        for(int i = 0; i < k; i++)

        {

            scanf("%d%d",&ss[i].x,&ss[i].y);

            ss[i].x--;

            ss[i].y--;

            p[i] = i;

            Case *= i+1;

        }

        int ans = -1;

        while(Case--)

        {

            int temp = bfs();

           // cout<<temp<<endl;

            if(temp > -1 && (temp < ans || ans == -1)) ans = temp;

            next_permutation(p,p+k);

        }

        printf("%d\n",ans);

    }

    return 0;

}