day-16.cpp

/*
Question: 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:

Any left parenthesis '(' must have a corresponding right parenthesis ')'.
Any right parenthesis ')' must have a corresponding left parenthesis '('.
Left parenthesis '(' must go before the corresponding right parenthesis ')'.
'*' could be treated as a single right parenthesis ')' or a single left parenthesis '(' or an empty string.
An empty string is also valid.



Example 1:
Input: "()"
Output: True
Example 2:
Input: "(*)"
Output: True
Example 3:
Input: "(*))"
Output: True
Note:
The string size will be in the range [1, 100].
*/

// O(N) & O(1) beats 100% cpp solution
class Solution {
   public:
    bool checkValidString(string s) {
        int balance = 0;
        for (int i = 0; i < s.length(); i++) {
            if (s[i] == ')')
                balance -= 1;
            else
                balance += 1;

            if (balance < 0) return false;
        }

        if (balance == 0) return true;

        balance = 0;
        for (int i = s.length() - 1; i >= 0; i--) {
            if (s[i] == '(')
                balance -= 1;
            else
                balance += 1;

            if (balance < 0) return false;
        }

        return true;
    }
};