[Python3] prefix min
Please check out this commit for solutions of weekly 260. \n\nclass Solution:\n    def maximumDifference(self, nums: List[int]) -> int:\n        ans = -1 \n    
Please check out this [commit](https://github.com/gaosanyong/leetcode/commit/fa0bb65b4cb428452e2b4192ad53e56393b8fb8d) for solutions of weekly 260. \n```\nclass Solution:\n    def maximumDifference(self, nums: List[int]) -> int:\n        ans = -1 \n        prefix = inf\n        for i, x in enumerate(nums): \n            if i and x > prefix: ans = max(ans, x - prefix)\n            prefix = min(prefix, x)\n        return ans \n```
['Python3']