AsFarFromLand.py

def maxDistance(self, grid):

        rows = len(grid)
        if rows == 0:
            return -1
        
        cols = len(grid[0])
        lands = collections.deque()
        
        maxDistance = 0
        
        # Cover up all the lands and say there nearest distance to themselves is = 0
        for i in range(rows):
            for j in range(cols):
                if grid[i][j] == 1:
                    lands.append([(i,j), 0])
                    
        while lands:
            for _ in range(len(lands)):

                # Get the node and the distance value corresponding to it
                temp = lands.popleft()
                x,y = temp[0] 
                d = temp[1]

                # Keep a global maxDistance check
                maxDistance = max(maxDistance, d)
                
                # Explore everything around the given land mass
            for dx, dy in [(1,0), (-1,0), (0,1), (0,-1)]:
                    xx, yy = x + dx, y + dy
                    # Simple edge cases tested
                    if xx < 0 or xx == rows or yy < 0 or yy == cols:
                        continue
                    # If you find a sea around it
                    if grid[xx][yy] == 0:
                    # Mutate and append
                        grid[xx][yy] = d + 1
                        lands.append([(xx, yy), d + 1])
                        
        return maxDistance or -1