Weighted Random Selection

Given an array of items, each with a corresponding weight, implement a function that randomly selects an item from the array, where the probability of selecting any item is proportional to its weight.

In other words, the probability of picking the item at index i is:
weights[i] / sum(weights).

Return the index of the selected item.

Example:

Input: weights = [3, 1, 2, 4]

Explanation:
sum(weights) = 10
3 has a 3/10 probability of being selected.
1 has a 1/10 probability of being selected.
2 has a 2/10 probability of being selected.
4 has a 4/10 probability of being selected.
For example, we expect index 0 to be returned 30% of the time.

Constraints:

• The weights array contains at least one element.