class Solution(object):
    def numIslands(self, grid):
        """
        :type grid: List[List[str]]
        :rtype: int
        """
        
        # DFS
        # Iterate through each of the cell and if it is an island, do dfs to mark all adjacent islands, then increase the counter by 1.
        if not grid:
            return 0
        
        res = 0
        for i in range(len(grid)):
            for j in range(len(grid[0])):
                if grid[i][j] == ‘1‘:
                    res += 1
                    self.dfs(grid, i, j)
                
        return res
    
    def dfs(self, grid, i, j):
        if i < 0 or j < 0 or i >= len(grid) or j >= len(grid[0]) or grid[i][j] != ‘1‘:
            return 
        
        grid[i][j] = ‘#‘
        self.dfs(grid, i+1, j)
        self.dfs(grid, i-1, j)
        self.dfs(grid, i, j+1)
        self.dfs(grid, i, j-1)