Find Largest Island (BFS)

[zafstojano]

What does this PR do?

This PR implements a procedural environment for finding the largest island in a binary grid (a popular Leetcode interview question).

An island is a group of 1's (representing land) connected 4-directionally (horizontal or vertical). One may assume all four edges of the grid are surrounded by water. The area of an island is the number of cells with a value 1 in the island.

The islands are generated with random walks starting from random positions in a grid initialized with 0's.

The result is obtained by doing Breadth First Search (BFS) from each position where there's a 1, without repeating already visited cells.

Because of the stochastic nature of the generation and merging of generated islands, it would be very hard to guarantee the actual minimum number of generated islands. Same reasoning can be applied for why it's hard to guarantee the maximum size for an individually generated island.

Nonetheless, I believe having a stricter upper bound on the number of generated islands (max_num_islands) is of largest importance for curriculum learning, hence why I didn't pursue these limitations any further.

Example usage

import reasoning_gym

# Defaults
# rows = 10  # Number of rows in the grid
# cols = 10  # Number of columns in the grid
# max_num_islands = 5  # Maximum number of islands (actual max might be smaller due to merging of islands during random walk)
# max_island_size = 10  # Maximum size of an island (actual max might be larger due to merging of islands during random walk)

data = reasoning_gym.create_dataset("largest_island", size=3, seed=42)

for i, item in enumerate(data):
    print(f"Example {i+1}:")
    print(f"Question: {item['question']}")
    print(f"Answer: {item['answer']}\n")
    print(f"Metadata: {item['metadata']}\n")

Example 1:
Question: You are given the following 10 x 10 binary matrix grid:
0 0 0 1 0 0 0 0 0 0
1 1 0 1 0 0 0 0 0 1
0 1 0 1 1 0 0 0 0 1
0 1 0 0 0 0 0 0 0 1
0 0 0 0 0 0 0 0 0 1
0 0 0 0 0 0 0 0 1 1
0 0 0 0 0 0 0 0 1 0
0 0 0 0 0 0 0 0 1 0
1 1 0 1 1 0 0 0 1 1
1 1 1 1 1 0 0 0 0 0

An island is a group of 1's (representing land) connected 4-directionally (horizontal or vertical).
You may assume all four edges of the grid are surrounded by water.

The area of an island is the number of cells with a value 1 in the island.

Return the maximum area of an island in grid. If there is no island, return 0.

Answer: 10

Metadata: {'grid': [[0, 0, 0, 1, 0, 0, 0, 0, 0, 0], [1, 1, 0, 1, 0, 0, 0, 0, 0, 1], [0, 1, 0, 1, 1, 0, 0, 0, 0, 1], [0, 1, 0, 0, 0, 0, 0, 0, 0, 1], [0, 0, 0, 0, 0, 0, 0, 0, 0, 1], [0, 0, 0, 0, 0, 0, 0, 0, 1, 1], [0, 0, 0, 0, 0, 0, 0, 0, 1, 0], [0, 0, 0, 0, 0, 0, 0, 0, 1, 0], [1, 1, 0, 1, 1, 0, 0, 0, 1, 1], [1, 1, 1, 1, 1, 0, 0, 0, 0, 0]], 'solution': 10}

Example 2:
Question: You are given the following 10 x 10 binary matrix grid:
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0

An island is a group of 1's (representing land) connected 4-directionally (horizontal or vertical).
You may assume all four edges of the grid are surrounded by water.

The area of an island is the number of cells with a value 1 in the island.

Return the maximum area of an island in grid. If there is no island, return 0.

Answer: 0

Metadata: {'grid': [[0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0]], 'solution': 0}

Example 3:
Question: You are given the following 10 x 10 binary matrix grid:
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
1 1 0 0 0 0 0 0 0 0
1 0 0 0 0 0 0 0 0 0
0 0 0 0 0 1 0 0 0 0
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 1 0
0 0 0 0 0 0 0 0 0 0

An island is a group of 1's (representing land) connected 4-directionally (horizontal or vertical).
You may assume all four edges of the grid are surrounded by water.

The area of an island is the number of cells with a value 1 in the island.

Return the maximum area of an island in grid. If there is no island, return 0.

Answer: 3

Metadata: {'grid': [[0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [1, 1, 0, 0, 0, 0, 0, 0, 0, 0], [1, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 1, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 1, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0]], 'solution': 3}

[andreaskoepf]

Very nice, thanks a lot! :-)