678. Valid Parenthesis String

最新推荐文章于 2020-09-14 21:01:30 发布

SHURamos

最新推荐文章于 2020-09-14 21:01:30 发布

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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

class Solution {
    public boolean checkValidString(String s) {
        Stack<Integer> st1 = new Stack<>();
		Stack<Integer> st2 = new Stack<>();
		for (int i = 0; i < s.length(); ++i) {
			char c = s.charAt(i);
			if (c == '(')
				st1.add(i);
			else if (c == '*')
				st2.add(i);
			else {
				if (!st1.isEmpty())
					st1.pop();
				else if (!st2.isEmpty())
					st2.pop();
				else 
					return false;
			}
		}
		while (!st1.isEmpty()) {
			int n1 = st1.pop();
			if (st2.isEmpty())
				return false;
			int n2 = st2.pop();
			if (n1 > n2)
				return false;
		}
		return true;
    }
}