input: Write a function to implement a binary search algorithm that efficiently finds an item in a sorted list of items. The function should return the index of the item if found, otherwise return -1. The function should work as follows:
  assert binary_search([3, 4, 5, 6, 7, 8, 9], 8)==5
  assert binary_search([3, 4, 5, 6, 7, 8, 9], 10)==-1
  assert binary_search([], 8)==-1
  assert binary_search([1, 2, 3, 4, 5], 1)==0
  assert binary_search([1, 2, 3, 4, 5], 5)==4
output: def binary_search(arr, target):
      left, right = 0, len(arr) - 1
      while left <= right:
          mid = (left + right) // 2
          if arr[mid] == target:
              return mid
          elif arr[mid] < target:
              left = mid + 1
          else:
              right = mid - 1
      return -1