P1451 求细胞数量

#include <bits/stdc++.h>
using namespace std;
const int maxn = 105;
int n, k, m;
int a[maxn][maxn];
int vis[maxn][maxn]; // 记录是否已被计算过
int num = 0;
int dx[5] = {-1, 0, 0, 1}; // 下，右，左，上
int dy[5] = {0, 1, -1, 0};
void dfs(int x, int y) // 已经选到了i,j
{
   vis[x][y] = 1;
   for (int i = 0; i < 4; i++)
   {
      int nx = x + dx[i];
      int ny = y + dy[i];
      if (a[nx][ny] == 0 || vis[nx][ny] == 1)
         continue;
      dfs(nx, ny);
   }
}
int main()
{
   cin >> n >> m;
   for (int i = 1; i <= n; i++)
   {
      for (int j = 1; j <= m; j++)
      {
         char u;
         cin >> u;
         a[i][j] = u - '0';
      }
   }
   for (int i = 1; i <= n; i++)
   {
      for (int j = 1; j <= m; j++)//每个位置都要dfs
      {
         if (a[i][j] != 0 && vis[i][j] == 0)
         {
            dfs(i, j);
            num++;
         }
      }
   }
   cout << num;
}