摘要： Given a string containing just the characters and , find the length of the longest valid (well formed) parentheses substring. For , the longest valid 阅读全文

摘要： Implement a basic calculator to evaluate a simple expression string. The expression string may contain open ( and closing parentheses ), the plus + or 阅读全文

摘要： Given a sorted array consisting of only integers where every element appears twice except for one element which appears once. Find this single element 阅读全文