摘要：Given a positive integer, return its corresponding column title as appear in an Excel sheet. For example: 很惭愧，这一题我没折腾出来。刚刚做了她的姐妹题，是把字母转化成数字，但是反过来就很难搞了 阅读全文

摘要：Implement atoi to convert a string to an integer. Hint: Carefully consider all possible input cases. If you want a challenge, please do not see below 阅读全文

摘要：Given two strings s and t which consist of only lowercase letters. String t is generated by random shuffling string s and then add one more letter at 阅读全文

摘要：Calculate the sum of two integers a and b, but you are not allowed to use the operator + and -. Example:Given a = 1 and b = 2, return 3. 个人思路：绕开+、-，利用 阅读全文