# Python List Exercises

These exercises will help you get really good at using lists in Python. You'll practice things like loops, slicing, grouping, and working with nested lists.

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## Exercise 1

**Flatten a Nested List**

### Problem

Write a function `flatten_list(nested_list)` that takes a list which may contain nested lists of any depth, and returns a single, flat list.

### Example

```python
flatten_list([1, [2, 3], [4, [5, 6], 7]])
# Output: [1, 2, 3, 4, 5, 6, 7]
```

### Concepts

- Recursion
- `isinstance` type checking
- `extend` vs `append`

---

## Exercise 2

**Group Consecutive Duplicates**

### Problem

Write a function `group_consecutive(lst)` that groups consecutive identical elements into sublists.

### Example

```python
group_consecutive([1, 1, 2, 2, 2, 3, 1, 1])
# Output: [[1, 1], [2, 2, 2], [3], [1, 1]]
```

### Concepts

- Iteration with state tracking
- Temporary sublists
- `for` loops with conditionals

---

## Exercise 3

**Rotate List k Times**

### Problem

Write a function `rotate_list(lst, k)` that rotates the list **right** by `k` steps.

> BONUS: Support negative `k` to rotate left.

### Example

```python
rotate_list([1, 2, 3, 4, 5], 2)
# Output: [4, 5, 1, 2, 3]
```

### Concepts

- Identify concepts yourself.

---

## Exercise 4

**List Difference by Value and Order**

### Problem

Write a function `diff_lists(a, b)` that removes **each occurrence** in `b` from `a`, respecting the number of times elements occur.

### Example

```python
diff_lists([1, 2, 2, 3, 4], [2, 4])
# Output: [1, 2, 3]
```

> One `2` and the `4` are removed. The second `2` remains.

### Concepts
- Element-by-element removal
- List copying
- `in` with deletion logic

---

## ✅ Pro Tips

- Try solving without using libraries.
- Then try versions using `collections.Counter`, `itertools`, or `functools` for practice.

- Write unit tests for edge cases:
  - Empty lists
  - Deep nesting
  - Large `k` values
  - Negative numbers