numberofislands.py

'''
Given an m x n 2D binary grid grid which represents a map of '1's (land) and '0's (water), return the number of islands.

An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may assume all four edges of the grid are all surrounded by water.

'''

class Solution:
    def numIslands(self, grid: List[List[str]]) -> int:
        if not grid:
            return 0
        
        rowNumber = len(grid)
        columnNumber = len(grid[0])
        
        visited = set()
        
        islandCounter = 0
        
        def bfs(row,column):
            myQueue = []
            
            visited.add((row,column))
            myQueue.append((row,column))
            
            
            while len(myQueue) != 0:
                row,column = myQueue.pop(0)
                myDirections = [[1,0],[-1,0],[0,1],[0,-1]]
                
                for rowDirection, columnDirection in myDirections:
                    newRow = row + rowDirection
                    newColumn = column + columnDirection
                    
                    if(newRow in range(rowNumber) and
                      newColumn in range(columnNumber) and
                       grid[newRow][newColumn] == "1" and
                       (newRow, newColumn) not in visited):
                        myQueue.append((newRow, newColumn))
                        visited.add((newRow, newColumn))
                        
            
        for row in range(rowNumber):
            for column in range(columnNumber):
                if grid[row][column] == "1" and (row,column) not in visited:
                    bfs(row,column)
                    islandCounter += 1
                        
        return islandCounter