678. Valid Parenthesis String

Problem Link

Description

---

Given a string s containing only three types of characters: '(', ')' and '*', return true if s is valid.

The following rules define a valid string:

• 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 "".

 

Example 1:

Input: s = "()"
Output: true

Example 2:

Input: s = "(*)"
Output: true

Example 3:

Input: s = "(*))"
Output: true

 

Constraints:

• 1 <= s.length <= 100
• s[i] is '(', ')' or '*'.

Solution

---

Python3

class Solution:
    def checkValidString(self, s: str) -> bool:
        N = len(s)
        cmin = cmax = 0
 
        for x in s:
            if x == "(":
                cmin += 1
                cmax += 1
            elif x == ")":
                cmin -= 1
                cmax -= 1
            else:
                cmin -= 1
                cmax += 1
 
            if cmax < 0: return False
 
            cmin = max(0, cmin)
        
        return cmin == 0

Java

class Solution {
   public boolean checkValidString(String s) {
        int low = 0;
        int high = 0;
        for (int i = 0; i < s.length(); i++) {
            if (s.charAt(i) == '(') {
                low++;
                high++;
            } else if (s.charAt(i) == ')') {
                if (low > 0) {
                    low--;
                }
                high--;
            } else {
                if (low > 0) {
                    low--;
                }
                high++;
            }
            if (high < 0) {
                return false;
            }
        }
        return low == 0;
    }
}