678. Valid Parenthesis String

1. Question

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 "".

2. Examples

Example 1:

Input: s = "()"
Output: true

Example 2:

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

Example 3:

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

3. Constraints

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

4. References

来源：力扣（LeetCode） 链接：https://leetcode-cn.com/problems/valid-parenthesis-string 著作权归领扣网络所有。商业转载请联系官方授权，非商业转载请注明出处。

5. Solutions

class Solution {
    public boolean checkValidString(String s) {
        Stack<Integer> left = new Stack<>();
        Stack<Integer> star = new Stack<>();
        for (int i = 0; i < s.length(); i++) {
            char ch = s.charAt(i);
            if (ch == '(') {
                left.push(i);
            } else if (ch == '*') {
                star.push(i);
            } else {
                if (!left.isEmpty()) {
                    left.pop();
                } else if (!star.isEmpty()) {
                    star.pop();
                } else {
                    return false;
                }
            }
        }

        while (!left.isEmpty() && !star.isEmpty()) {
            if (left.pop() > star.pop()) {
                return false;
            }
        }
        return left.isEmpty();
    }
}