Add edge cases for equilibrium index

@@ -1,54 +1,62 @@ """ Find the Equilibrium Index of an Array.-Reference: https://www.geeksforgeeks.org/equilibrium-index-of-an-array/ -Python doctest can be run with the following command:-python -m doctest -v equilibrium_index_in_array.py--Given a sequence arr[] of size n, this function returns-an equilibrium index (if any) or -1 if no equilibrium index exists.--The equilibrium index of an array is an index such that the sum of-elements at lower indexes is equal to the sum of elements at higher indexes.+Reference:+https://www.geeksforgeeks.org/equilibrium-index-of-an-array +Python doctest can be run with: +python -m doctest -v equilibrium_index_in_array.py -Example Input:-arr = [-7, 1, 5, 2, -4, 3, 0]-Output: 3+Given an array arr of size n, return an equilibrium index+if one exists; otherwise return -1. +An equilibrium index is an index where the sum of all+elements to the left equals the sum of all elements+to the right. """   def equilibrium_index(arr: list[int]) -> int:     """-    Find the equilibrium index of an array.-+    Find the first equilibrium index of an array.     Args:-        arr (list[int]): The input array of integers.-+        arr: The input array of integers.     Returns:-        int: The equilibrium index or -1 if no equilibrium index exists.-+        The first equilibrium index, or -1 if none exists.     Examples:+        >>> equilibrium_index([])+        -1+        >>> equilibrium_index([5])+        0         >>> equilibrium_index([-7, 1, 5, 2, -4, 3, 0])         3+        >>> equilibrium_index([2, 4, 6, 8, 10, 3])+        -1         >>> equilibrium_index([1, 2, 3, 4, 5])         -1         >>> equilibrium_index([1, 1, 1, 1, 1])         2-        >>> equilibrium_index([2, 4, 6, 8, 10, 3])-        -1+        >>> equilibrium_index([0, 0, 0])+        0+        >>> equilibrium_index([-1, -1, -1])+        1+        >>> equilibrium_index([1, -1, 0])+        2++    Time Complexity:+        O(n), where n is the length of the array.++    Space Complexity:+        O(1), using only constant extra space.     """     total_sum = sum(arr)     left_sum = 0-     for i, value in enumerate(arr):         total_sum -= value         if left_sum == total_sum:             return i         left_sum += value-     return -1