```
public int numIslands(char[][] grid) {
if(grid == null) return 0;
int count = 0;
for (int i = 0; i < grid.length; i++) {
for (int j = 0; j < grid[0].length; j++) {
if (grid[i][j] == '0') continue;
count++;
clearIsland(grid, grid.length, grid[0].length, i, j);
}
}
return count;
}
private void clearIsland(char[][] grid, int row, int column, int i, int j) {
if(i < 0 || j < 0 || i == row || j == column || grid[i][j] == '0') return;
grid[i][j] = '0';
clearIsland(grid, row, column, i, j + 1);
clearIsland(grid, row, column, i + 1, j);
clearIsland(grid, row, column, i - 1, j);
clearIsland(grid, row, column, i, j - 1);
}
```