摘要：
https://pintia.cn/problem-sets/994805342720868352/problems/994805478658260992 Notice that the number 123456789 is a 9-digit number consisting exactly 阅读全文
摘要：
https://pintia.cn/problem-sets/994805342720868352/problems/994805487143337984 A number that will be the same when it is written forwards or backwards 阅读全文
摘要：
https://pintia.cn/problem-sets/994805342720868352/problems/994805511923286016 The highest building in our city has only one elevator. A request list i 阅读全文
摘要：
https://pintia.cn/problem-sets/994805342720868352/problems/994805444361437184 Being unique is so important to people on Mars that even their lottery i 阅读全文
摘要：
https://pintia.cn/problem-sets/994805342720868352/problems/994805454989803520 To prepare for PAT, the judge sometimes has to generate random passwords 阅读全文
摘要：
https://pintia.cn/problem-sets/994805342720868352/problems/994805422639136768 Behind the scenes in the computer's memory, color is always talked about 阅读全文
摘要：
https://pintia.cn/problem-sets/994805342720868352/problems/994805429018673152 Given two strings S~1~ and S~2~, S = S~1~ - S~2~ is defined to be the re 阅读全文