题目链接：

https://www.acwing.com/problem/content/1115/

想要去掉DFS里的位移for循环改为:dfs(x+1,y);vis(x+1,y)=flase;. .. 这样的一维位移形式；

for循环写法：

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

using namespace std;
const int N = 25;
int n, m;
char g[N][N];
bool st[N][N];

int dx[4] = {-1, 0, 1, 0};
int dy[4] = {0, 1, 0, -1};

int dfs(int x, int y)
{
    int cnt = 1;
    st[x][y] = true;
    for (int i = 0; i < 4; i++)
    {
        int a = x + dx[i];
        int b = y + dy[i];
        if (a < 0 || a >= n || b < 0 || b >= m)
        {
            continue;
        }
        if (g[a][b] != '.')
        {
            continue;
        }
        if (st[a][b] == true)
        {
            continue;
        }

        cnt = cnt + dfs(a, b);
    }
    return cnt;
}

int main()
{
    while (1)
    {
        cin >> m >> n;
        if (n == 0 && m == 0)
        {
            break;
        }
        for (int i = 0; i < n; i++)
        {
            cin >> g[i];
        }

        int x, y;
        for (int i = 0; i < n; i++)
        {
            for (int j = 0; j < m; j++)
            {
                if (g[i][j] == '@')
                {
                    x = i;
                    y = j;
                }
            }
        }
        memset(st, 0, sizeof(st));
        cout << dfs(x, y) << endl;
    }
    // 核心代码

    // system("pause");
    return 0;
}