摘要： Given an integer n, count the total number of digit 1 appearing in all non-negative integers less than or equal to n. For example:Given n = 13,Return 阅读全文

摘要： 231. Power of Two Given an integer, write a function to determine if it is a power of two. 342. Power of Four Given an integer (signed 32 bits), write 阅读全文

摘要： 判断两个字符串相同要用isEqualToString函数，只用“==”判断，结果会错误。 阅读全文