Number of Islands

from collections import deque
class Solution:
    def numIslands(self, grid: List[List[str]]) -> int:
        rowN = len(grid)
        colN = len(grid[0])
        
        dx = [0,0,-1,1]
        dy = [-1,1,0,0]
        
        count = 0
        
        for i in range(rowN):
            for j in range(colN):
                if grid[i][j] == "1":
                    count += 1
                    q = deque()
                    grid[i][j] = "0"
                    q.append([i,j])
                    while q:
                        r, c = q.popleft()
                        for k in range(4):
                            x = r+dx[k]
                            y = c+dy[k]
                            if 0<=x<rowN and 0<=y<colN and grid[x][y] == "1":
                                q.append([x,y])
                                grid[x][y] = "0"
        return count