Write a function cumulative_sum(arr) that returns the cumulative (prefix) sum of an array. Each element at index i in the output is the sum of all elements from index 0 to i.
Example:
Input: arr = [1, 2, 3, 4, 5]
Output: [1, 3, 6, 10, 15]
**Explanation:** [1, 1+2, 1+2+3, 1+2+3+4, 1+2+3+4+5]
Constraints:
Test Cases
Test Case 1
Input:
[1, 2, 3, 4, 5]Expected:
[1, 3, 6, 10, 15]Test Case 2
Input:
[5, 5, 5]Expected:
[5, 10, 15]Test Case 3
Input:
[10]Expected:
[10]+ 2 hidden test cases