[Python3] Straightforward O(n) no extra space w comments
```py\nclass Solution:\n    def maximumDifference(self, nums: List[int]) -> int:\n        output = -1\n        low = 10**9 # Set because of question constraints
```py\nclass Solution:\n    def maximumDifference(self, nums: List[int]) -> int:\n        output = -1\n        low = 10**9 # Set because of question constraints\n        \n        for i in range(len(nums)):\n            # If we come across a new lowest number, keep track of it\n            low = min(low, nums[i])\n            \n            # If the current number is greater than our lowest - and if their difference is greater than\n            # the largest distance seen yet, save this distance\n            if nums[i] > low: output = max(output, nums[i] - low)\n        return output
['Python', 'Python3']