// flood fill
class Solution {
public:
vector<vector<char>> g;
int dx[4] = {-1, 0, 1, 0}, dy[4] = {0, 1, 0, -1};
void dfs(int x, int y) {
g[x][y] =0;
for (int i = 0; i < 4; ++i) {
int a = x + dx[i], b = y + dy[i];
if (a >= 0 && a < g.size() && b >= 0 && b < g[a].size() && g[a][b] == '1') {
dfs(a ,b);
}
}
}
int numIslands(vector<vector<char>>& _g) {
g = _g;
int cnt = 0;
for (int i = 0; i < g.size(); ++i) {
for (int j = 0; j < g[i].size(); ++j) {
if (g[i][j] == '1') {
dfs(i, j);
cnt++;
}
}
}
return cnt;
}
};