678. Valid Parenthesis String

Problem

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 (Java)

class Solution {
    public boolean checkValidString(String s) {
        int lo = 0;
        int hi = 0;
        for (int i = 0; i < s.length(); i++) {
            lo += s.charAt(i) == '(' ? 1 : -1;
            hi += s.charAt(i) != ')' ? 1 : -1;
            if (hi < 0) {
                break;
            }
            lo = Math.max(0, lo);
        }
        return lo == 0;
    }
}

Explain:

nope.

Complexity:

• Time complexity : O(n).
• Space complexity : O(n).