#include<iostream>
#include<string.h>
#include<queue>
using namespace std;
struct id
{
	int x,y,s;
};
queue<id>q;
int n,m,x,y,sx,sy,ans,k;
int xx[8]={-1,-1,-1,0,0,1,1,1};
int yy[8]={-1,0,1,-1,1,-1,0,1};
bool qp[110][110];
char ch;
int main()
{
	memset(qp,false,sizeof(qp));
	cin>>m>>n>>x>>y;
	for(int i=1;i<=n;i++)
	{
		for(int j=1;j<=m;j++)
		{
			cin>>ch;
			if(ch=='.')qp[i][j]=true;
		}
	}
	sy=x;
	sx=n-y+1;
	q.push(id{sx,sy,0});
	qp[sx][sy]=false;
	while(!q.empty())
	{
		int tx=q.front().x;
		int ty=q.front().y;
		ans=q.front().s;
		q.pop();
		for(int i=0;i<8;i++)
		{
			int nx=tx+xx[i];
			int ny=ty+yy[i];
			if(qp[nx][ny])
			{
				q.push(id{nx,ny,ans+1});
				qp[nx][ny]=false;
			}
		}
	}
	cout<<ans;
	return 0;
}

不用广搜,直接暴力居然可以AC

#include <iostream>
using namespace std;

char a[101][101];
int m,n,x,y;

void kuo()
{
	for(int i = 1;i <= n;i++)
	{
		for(int j = 1;j <= m;j++)
		{
			if(a[i][j] == 'M')
			{
				if(a[i][j + 1] == '.') a[i][j + 1] = 'A';
				if(a[i][j - 1] == '.') a[i][j - 1] = 'A';
				if(a[i + 1][j] == '.') a[i + 1][j] = 'A';
				if(a[i - 1][j] == '.') a[i - 1][j] = 'A';
				
				if(a[i + 1][j + 1] == '.') a[i + 1][j + 1] = 'A';
				if(a[i - 1][j + 1] == '.') a[i - 1][j + 1] = 'A';
				if(a[i - 1][j - 1] == '.') a[i - 1][j - 1] = 'A';
				if(a[i + 1][j - 1] == '.') a[i + 1][j - 1] = 'A';
			}
		}
	}
	for(int i = 1;i <= n;i++)
	{
		for(int j = 1;j <= m;j++)
		{
			if(a[i][j] == 'A')
			{
				a[i][j] = 'M';
			}
		}
	}
}

bool check()
{
	for(int i = 1;i <= n;i++)
	{
		for(int j = 1;j <= m;j++)
		{
			if(a[i][j] == '.')
			{
				return false;
			}
		}
	}
	return true;
}

int main()
{
	cin >> m >> n >> x >> y;
	for(int i = 1;i <= n;i++)
	{
		for(int j = 1;j <= m;j++)
		{
			cin >> a[i][j];
		}
	}
	a[n - y + 1][x] = 'M';
	for(int ans = 0;;ans++)
	{
		if(check())
		{
			cout << ans << endl;
			return 0;
		}
		kuo();
	}
	return 0;
}

名副其实的广搜题， 但是我仍然不会 废话不多说，直接上代码

#include <iostream>
#include <queue>
using namespace std;
int r, c, x, y;
int dir[8][2] = { {-1, 0}, {1, 0}, {0, -1}, {0, 1}, {-1, -1}, {1, -1}, {-1, 1}, {1, 1}};
char ma[105][105];
bool vis[105][105];
int ans = 0;
struct node{
	int x, y, s;
};
queue<node > q;
void bfs(int x, int y){
	vis[x][y] = 1;
	q.push((node){x, y, 0});
	while(!q.empty()){
		node p = q.front();
		q.pop();
		ans = max(ans, p.s);
		for(int i=0; i<8; i++){
			int nx = p.x + dir[i][0];
			int ny = p.y + dir[i][1];
			if(1 <= nx && nx <= r && 1 <= ny && ny <= c){
				if(vis[nx][ny] == 0 && ma[nx][ny] != '*'){
					vis[nx][ny] = 1;
					q.push((node){nx, ny, p.s + 1});
				}
			}
		}
	}
}
int main(){
	cin>>c>>r>>x>>y;
	for(int i=1; i<=r; i++){
		for(int j=1; j<=c; j++){
			cin>>ma[i][j];
		}
	}
	bfs(r - y + 1, x);
	cout<<ans<<endl;
}

#include<iostream>  
#include<cstring>  
#include<cstdio>  
using namespace std;  
int sx[8]={1,1,1,0,0,-1,-1,-1};  
int sy[8]={-1,0,1,-1,1,-1,0,1};  
int x,y,mx,my,nowx,nowy,nowstep,head,tail,n,m,ans;  
char s[105];  
struct hp{  
    int x,y,step;  
}queue[10005];  
int a[105][105];   
int main(){  
    scanf("%d%d%d%d\n",&n,&m,&mx,&my);  
    swap(n,m); swap(mx,my);  
    for (int i=1;i<=n;++i){  
        gets(s);  
        for (int j=1;j<=m;++j)  
          if (s[j-1]=='*') a[i][j]=1;  
    }  
    a[mx][my]=1;  
    head=0,tail=1,queue[tail].x=mx,queue[tail].y=my;  
    while (head<tail){  
        head++;  
        nowx=queue[head].x,nowy=queue[head].y,nowstep=queue[head].step;  
        for (int i=0;i<8;++i){  
            x=nowx+sx[i],y=nowy+sy[i];  
            if (x>0&&x<=n&&y>0&&y<=m&&!a[x][y]){  
                a[x][y]=1;  
                tail++;  
                queue[tail].x=x,queue[tail].y=y;  
                queue[tail].step=nowstep+1;  
                ans=max(ans,queue[tail].step);  
            }  
        }  
    }  
    printf("%d",ans);  
}

C++ :

#include<iostream>
#include<algorithm>
#include<queue>
using namespace std;
const int maxn = 120;
int X, Y, Mx, My;
struct node{
    int r,c,s;
    node(int r,int c,int s):r(r),c(c),s(s){}
};
int dir[][2]={{0,1},{0,-1},{1,0},{-1,0},{1,1},{1,-1},{-1,1},{-1,-1}};
char m[maxn][maxn];
bool visited[maxn][maxn];
int s;
void bfs(int r, int c)
{
    queue<node> q;
    visited[r][c] = true;
    q.push(node(r, c, 0));
    while(!q.empty()){
        const node&cur=q.front();
        s=cur.s;
        for(int i=0;i<8; ++i){
            int nr = cur.r + dir[i][0];
            int nc = cur.c + dir[i][1];
            if(0 < nr && nr <= Y && 0 < nc && nc <= X)
                if(m[nr][nc] == '.' && !visited[nr][nc]){
                    visited[nr][nc] = true;
                    q.push(node(nr, nc, cur.s + 1));
                }
        }
        q.pop();
    }
} 
int main(){
    cin>>X>>Y>>Mx>>My;
    for(int i=Y;i>0;--i)
        for(int j=0;j<X;)
            cin>>m[i][++j];
    bfs(My,Mx);
    cout<<s;
    return 0;
}