Leetcode[day16] - Valid Parenthesis String

Given a string containing only three types of characters: '(', ')' and '*', write a function to check whether this string is valid. We define the validity of a string by these rules: 1. Any left parenthesis '(' must have a corresponding right parenthesis ')'. 2. Any right parenthesis ')' must have a corresponding left parenthesis '('. 3. Left parenthesis '(' must go before the corresponding righ..