Question: 
Write a function to find the equilibrium index of the given array.


Model's Code:
def equilibrium_index(arr):
    total_sum = sum(arr)
    left_sum = 0
    
    for i, num in enumerate(arr):
        total_sum -= num
        if left_sum == total_sum:
            return i
        left_sum += num
    
    return -1



Sample Correct Code:
def equilibrium_index(arr):
  total_sum = sum(arr)
  left_sum=0
  for i, num in enumerate(arr):
    total_sum -= num
    if left_sum == total_sum:
      return i
    left_sum += num
  return -1


Asserts:
assert equilibrium_index([1, 2, 3, 4, 1, 2, 3]) == 3
assert equilibrium_index([-7, 1, 5, 2, -4, 3, 0]) == 3
assert equilibrium_index([1, 2, 3]) == -1


Tests:
Test 1 of 3: PASS
Test 2 of 3: PASS
Test 3 of 3: PASS

Test 701 of 974: 529/701 (75.46362339514978%): success