摘要：
Given a non-empty string check if it can be constructed by taking a substring of it and appending multiple copies of the substring together. You may a 阅读全文
摘要：
Given a non-negative integer represented as a non-empty array of digits, plus one to the integer. You may assume the integer do not contain any leadin 阅读全文
摘要：
Given two non-negative integers num1 and num2 represented as string, return the sum of num1 and num2. Note: 这道题不能用long会越界，所以只能用string直接来append。精髓在于设置一 阅读全文