Reason About Alternating Positive and Negative Values

Question

The candidate is asked to implement a solution that rearranges an array of integers such that positive and negative values alternate, starting with a positive number if available.

Codemia · Accepted Answer

To solve the problem of rearranging the array with alternating positive and negative values, we can utilize a two-pointer technique. We will maintain two pointers: one for the positive numbers and one for the negative numbers. The goal is to create a new array where we alternate between these two types of numbers.

1. Initialize two lists: one for positive numbers and one for negative numbers.
2. Iterate through the input array and populate the two lists accordingly.
3. Create a new array to hold the result.
4. Use a loop to fill the new array by alternating between the positive and negative lists until one of them runs out of elements.
5. If any elements remain in either list, append them to the end of the result array.

The time complexity of this approach is O(n), where n is the number of elements in the input array, as we traverse the array a constant number of times. The space complexity is also O(n) due to the additional lists used to store positive and negative numbers.

Here's a sample implementation in Python:
```python
def rearrange_array(arr):
    positives = []
    negatives = []
    for num in arr:
        if num >= 0:
            positives.append(num)
        else:
            negatives.append(num)

result = []
    pos_index, neg_index = 0, 0
    while pos_index < len(positives) and neg_index < len(negatives):
        result.append(positives[pos_index])
        result.append(negatives[neg_index])
        pos_index += 1
        neg_index += 1

result.extend(positives[pos_index:])
    result.extend(negatives[neg_index:])
    return result
```
This code effectively rearranges the input array as specified.

Consider scenarios where the input array may contain only positive numbers, only negative numbers, or be empty. In these cases, the output should reflect the input without any rearrangement, as there are no alternate values to interleave.

Reason About Alternating Positive and Negative Values

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