[LeetCode] 200. Number of Islands

 Problem : https://leetcode.com/problems/number-of-islands/

Use counter as flag to mark visited position.

class Solution:
    def numIslands(self, grid: List[List[str]]) -> int:
        row = len(grid)
        if not row:
            return 0
        
        column = len(grid[0])
        
        count = 2
        
        def dfs(y, x, mark):
            if y < 0 or y >= row:
                return
            
            if x < 0 or x >= column:
                return
            
            if grid[y][x] == "1":
                grid[y][x] = mark

                dfs(y-1, x, mark)
                dfs(y+1, x, mark)
                dfs(y, x-1, mark)
                dfs(y, x+1, mark)
            
        
        for y in range(row):
            for x in range(column):
                if grid[y][x] == "1":
                    dfs(y, x, str(count))
                    count += 1
        
        
        return count - 2