ural 1250

有点坑的dfs  看懂题应该就会做了 神圣海必然围成一个圈  dfs将神圣还外围的全部去掉   简单题 

#include <cstdio>
#include <cstring>
#include <algorithm>

using namespace std;
int dx[] = {1, 1, 1, -1, -1, -1, 0, 0};
int dy[] = {1, 0, -1, 0, 1, -1, 1, -1};
int ex[] = {1, -1, 0, 0};
int ey[] = {0, 0, 1, -1};
int g[510][510],w,h;
bool ok(int x, int y)
{
    if(x >= 1 && y >= 1 && x <= h && y <= w)
        return true;
    return false;
}
void dfs1(int x, int y)
{
    if(g[x][y] == 1)
    {
        g[x][y] = 2;
        for(int i = 0; i < 8; i++)
        {
            int nx = x+dx[i], ny = y+dy[i];
            if(ok(nx,ny))
                dfs1(nx, ny);
        }
    }
}
void dfs2(int x, int y)
{
    if(g[x][y] != 2 && g[x][y] != 3)
    {
        g[x][y] = 3;
        for(int i = 0; i < 4; i++)
        {
            int nx = x+ex[i], ny = y+ey[i];
            if(ok(nx,ny))
                dfs2(nx, ny);
        }
    }
}
void dfs3(int x, int y)
{
    if(g[x][y] == 0)
    {
        g[x][y] = 1;
        for(int i = 0; i < 4; i++)
        {
            int nx = x+ex[i], ny = y+ey[i];
            if(ok(nx,ny))
                dfs3(nx, ny);
        }
    }
}
int main()
{
    int x,y;
    char c;
    scanf("%d%d%d%d",&w,&h,&x,&y);
    getchar();
    memset(g, 0, sizeof(g));
    for(int i = 1; i <= h; i++)
    {
        for(int j = 1; j <= w; j++)
        {
            scanf("%c",&c);
            if(c == '.')
                g[i][j] = 1;
        }
        getchar();
    }
    dfs1(y, x);
    for(int i = 1; i <= w; i++)
    {
        if(g[1][i] != 2)
            dfs2(1, i);
        if(g[h][i] != 2)
            dfs2(h, i);
    }
    for(int i = 1; i <= h; i++)
    {
        if(g[i][1] != 2)
            dfs2(i, 1);
        if(g[i][w] != 2)
            dfs2(i, w);
    }
    int ans = 0;
    for(int i = 1; i <= h; i++)
        for(int j = 1; j <= w; j++)
        {
            if(!g[i][j])
            {
                dfs3(i, j);
                ans++;
            }
        }
    printf("%d\n",ans);
    return 0;
}