---
title: "LeetCode #200: Number of Islands"
url: https://perrotta.dev/2026/01/leetcode-%23200-number-of-islands/
last_updated: 2026-01-10
---


[LeetCode #200: Number of Islands](https://leetcode.com/problems/number-of-islands):

```python
class Solution:
    def numIslands(self, grid: List[List[str]]) -> int:
        m = len(grid)
        n = len(grid[0])

        def within_bounds(a, b):
            return 0 <= a < m and 0 <= b < n

        def dfs(x, y):
            if not within_bounds(x, y):
                return

            if grid[x][y] in ["-1", "0"]:
                return

            grid[x][y] = "-1"

            for dir in [(0, 1), (1, 0), (0, -1), (-1, 0)]:
                neighbor = (
                    x + dir[0],
                    y + dir[1],
                )
                dfs(neighbor[0], neighbor[1])

        ans = 0

        for x, row in enumerate(grid):
            for y, cell in enumerate(row):
                if grid[x][y] == "1":
                    dfs(x, y)
                    ans += 1

        return ans
```

Pass tuples around:

```python
class Solution:
    def numIslands(self, grid: List[List[str]]) -> int:
        m = len(grid)
        n = len(grid[0])

        def within_bounds(coords):
            (a, b) = coords
            return 0 <= a < m and 0 <= b < n

        def dfs(coords):
            (x, y) = coords
            if not within_bounds(coords):
                return

            if grid[x][y] in ["-1", "0"]:
                return

            grid[x][y] = "-1"

            for dir in [(0, 1), (1, 0), (0, -1), (-1, 0)]:
                neighbor = (
                    x + dir[0],
                    y + dir[1],
                )
                dfs(neighbor)

        ans = 0

        for x, row in enumerate(grid):
            for y, cell in enumerate(row):
                if grid[x][y] == "1":
                    dfs((x, y))
                    ans += 1

        return ans
```