Leetcode: Number of Islands, with algorithm for grouping the islands by ID

leetcode.number-of-islands.py

'''
This solves the Number of Islands problem in Leetcode, but also creates unique 
 incrementing integer IDs for each island, and tracks all the coordinates that
 make up each.
To solve the problem, you just return current_island_id + 1
To see the grouped islands by ID, return islands
Problem: https://leetcode.com/problems/number-of-islands
'''

class Solution:
    def numIslands(self, grid: List[List[str]]) -> int:
        LAND = '1'
        WATER = '0'
        rows = len(grid)
        cols = len(grid[0])

        current_island_id = -1
        visited = set()
        islands = {}

        st = []

        for ri in range(rows):
            for ci in range(cols):
                if grid[ri][ci] == LAND and not (ri,ci) in visited:
                    current_island_id += 1
                    islands[current_island_id] = set()
                    st.append((ri,ci))
                else:
                    visited.add((ri,ci))
                
                while st:
                    r, c = st.pop()
                    if (r,c) in visited:
                        continue
                    
                    visited.add((r,c))
                    if grid[r][c] == WATER:
                        continue
                    
                    islands[current_island_id].add((r,c))

                    if r > 0:
                        st.append((r-1,c))
                    if r < rows-1:
                        st.append((r+1,c))
                    if c > 0:
                        st.append((r,c-1))
                    if c < cols-1:
                        st.append((r,c+1))
        
        # To give the desired answer:
        # return current_island_id + 1

        # To see the islands that are now grouped:
        return islands