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678. Valid Parenthesis String

Difficulty Topics

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

valid-parenthesis-string.py
class Solution:
    def checkValidString(self, s: str) -> bool:

        cmin = cmax = 0
        for i in s:
            if i == '(':
                cmax += 1
                cmin += 1
            if i == ')':
                cmax -= 1
                cmin = max(cmin - 1, 0)
            if i == '*':
                cmax += 1
                cmin = max(cmin - 1, 0)
            if cmax < 0:
                return False
        return cmin == 0
valid-parenthesis-string.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;
    }
}