请在以下文本中查找并替换所有的人名（例如John Doe）和城市名（例如New York）为占位符（例如姓名和地点）。
文本：“John Doe lives in New York and works at Google. He is a computer science expert.”
[占位符] lives in [占位符] and works at Google. [占位符] is a computer science expert.