python solution
\nclass Solution(object):\n    def strWithout3a3b(self, A, B):\n        """\n        :type A: int\n        :type B: int\n        :rtype: str\n        """\n     
```\nclass Solution(object):\n    def strWithout3a3b(self, A, B):\n        """\n        :type A: int\n        :type B: int\n        :rtype: str\n        """\n        if A == 0:\n            return \'b\' * B\n        elif B == 0:\n            return \'a\' * A\n        elif A == B:\n            return \'ab\' + self.strWithout3a3b(A-1, B-1)\n        elif A > B:\n            return \'aab\' + self.strWithout3a3b(A-2, B-1)\n        else:\n            return \'bba\' + self.strWithout3a3b(A-1, B-2)\n```
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