Interview Course Based on Story Questions

## Problem statement

Given an `m x n` 2D grid 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 surrounded by water.


### Input
The input will be in the form of a 2D matrix. The following is an example input:

```python
grid = [
  ["1","1","0","0","0"],
  ["1","1","0","0","0"],
  ["0","0","1","0","0"],
  ["0","0","0","1","1"]
]
```

### Output
The output will be an integer representing the number of islands. The following is an example output:


```python
3
```

## Coding exercise
Implement the `num_islands(islands)` function, where `islands` is the 2D matrix of `1's` and `0's`. The function returns an integer representing the number of islands calculated from the matrix.

# Problem statement

Given an `m x n` 2D grid 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 surrounded by water.


## Input
The input will be in the form of a 2D matrix. The following is an example input:

```python
grid = [
  ["1","1","0","0","0"],
  ["1","1","0","0","0"],
  ["0","0","1","0","0"],
  ["0","0","0","1","1"]
]
```

## Output
The output will be an integer representing the number of islands. The following is an example output:


```python
3
```

# Coding exercise
Implement the `num_islands(islands)` function, where `islands` is the 2D matrix of `1's` and `0's`. The function returns an integer representing the number of islands calculated from the matrix.

DIY: Number of Islands

Problem statement