python easy solution, beats 100%
We use an array to record whether we need to compare\n\n\nfrom copy import copy\n\nclass Solution(object):\n    def minDeletionSize(self, A):\n        """\n    
We use an array to record whether we need to compare\n\n```\nfrom copy import copy\n\nclass Solution(object):\n    def minDeletionSize(self, A):\n        """\n        :type A: List[str]\n        :rtype: int\n        """\n        A_len, str_len, res = len(A), len(A[0]), 0\n        is_need_compare = [True] * A_len\n\n        for i in xrange(str_len):\n            tmp = copy(is_need_compare)\n            for j in xrange(1, A_len):\n                if is_need_compare[j]:\n                    if A[j][i] < A[j - 1][i]:\n                        res += 1\n                        is_need_compare = tmp\n                        break\n\n                    elif A[j][i] > A[j - 1][i]:\n                        is_need_compare[j] = False\n                            \n        return res\n```
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