练练脑子!!!

来源: 于 2012-07-12 09:34:56 [博客] [旧帖] [给我悄悄话] 本文已被阅读：次

The integers 1, 2, 3, ..., 50 are written down in any order. Show that one can delete 42 of them, so that an increasing or decreasing sequence remains.