问题分析:u75c5u4f8buu:u4f60u597duff0cuuu4e2duu4e34u5e8au4e0auu4e00u79cdu7c7bu578bu662fu8fdbu5c55uuu4e2duff0cu7ed3uu4f60uu63cfu8ff0uff0cu611fu89c9u60a3uu4e0duuu8fd9u79cdu7c7bu578buu53efu80fduuff0cu8fd9u65f6u5c31uu4f4fuu6cbbuuff0cu8f93u6db2u6cbbuu914duu53e3u670du836fuuff0cuu6b62u75c5u60c5u8fdbu4e00u6b65u52a0u91cdu610fu89c1u5efau8bae:u79efuuu836fuff0cu5c3du91cfu8ba9u75c5u60c5u7a33u5b9auff0cuuu6b7bu4e00u822cuu53d1u75c51uuu662fu4f1au51fau73b0u75c5uuu56f4u6c34u80bfuuff0cu75c5u60c5u4f1auu53d8uuff0cuu4f53uu590du7a0bu5ea6u56e0u75c5u53d8u90e8u4f4duuu6b7buu79efu800cu5f02