Find Last Position in Sorted Array

Write a Python function `last_position(arr, x)` that takes a sorted array `arr` and an integer `x` as input and returns the last position (0-based index) of the element `x` in the array. If the element is not present, return `-1`.

The function should use an efficient approach, such as binary search, to achieve a time complexity of O(log n).

#### Example Usage
```python [main.nopy]
print(last_position([1, 2, 2, 2, 3], 2))  # Output: 3
print(last_position([1, 2, 3, 4, 5], 6))  # Output: -1
print(last_position([1, 1, 1, 1, 1], 1))  # Output: 4
```

#### Constraints
- The input array `arr` is sorted in non-decreasing order.
- The array can contain duplicate elements.
- The function should handle empty arrays gracefully.
def last_position(arr, x):
    """
    Find the last position of x in a sorted array arr.

    Parameters:
    arr (list): A sorted list of integers.
    x (int): The target integer to find.

    Returns:
    int: The last position of x in arr, or -1 if x is not found.
    """
    # Implement the function using binary search
    pass
Intermediate
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