Python solution using set
\nimport random\nclass Solution(object):\n\n    def __init__(self, n_rows, n_cols):\n        """\n        :type n_rows: int\n        :type n_cols: int\n        
```\nimport random\nclass Solution(object):\n\n    def __init__(self, n_rows, n_cols):\n        """\n        :type n_rows: int\n        :type n_cols: int\n        """\n        self.row, self.col = n_rows, n_cols\n        self.flipped = set()\n        \n\n    def flip(self):\n        """\n        :rtype: List[int]\n        """\n        while True:\n            m, n = random.randint(0, self.row-1), random.randint(0, self.col-1)\n            if (m, n) not in self.flipped:\n                self.flipped.add((m, n))\n                return [m, n]\n        \n\n    def reset(self):\n        """\n        :rtype: void\n        """\n        self.flipped = set()\n```
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