摘要：
Eva loves to collect coins from all over the universe, including some other planets like Mars. One day she visited a universal shopping mall which cou 阅读全文
摘要：
Given two strings S1 and S2, S = S1 - S2 is defined to be the remaining string after taking all the characters in S2 from S1. Your task is simply to c 阅读全文
摘要：
Being unique is so important to people on Mars that even their lottery is designed in a unique way. The rule of winning is simple: one bets on a numbe 阅读全文
摘要：
Eva would like to make a string of beads with her favorite colors so she went to a small shop to buy some beads. There were many colorful strings of b 阅读全文
摘要：
On a broken keyboard, some of the keys are worn out. So when you type some sentences, the characters corresponding to those keys will not appear on sc 阅读全文