摘要：
The computer op erates on a single stack of sets, which is initially empty. After each op eration, thecardinality of the topmost set on the stack is o... 阅读全文
摘要：
Most crossword puzzle fans are used toanagrams--groups of words with the same letters in different orders--for example OPTS, SPOT, STOP, POTS and POST... 阅读全文