678 brackets effectiveness

Given a string containing only the three character classes :(,) and *, write a function to test whether the string is a valid string. Valid string has the following rules:

Any left parenthesis (must have a corresponding right parenthesis).
Any right parenthesis) must have a corresponding left parenthesis (.
Left parenthesis (must be before the corresponding right parenthesis).
* May be viewed as a single right parenthesis), or a single left parenthesis (or an empty string.
An empty string It is also considered a valid string.

Ideas:

The (and each stack, and then put regarded (traversing the string), then discuss as) case,
at this time (the index must be greater than before deemed)

class Solution {
    public boolean checkValidString(String s) {
        stack<int> left,star;
        for(int i=0;i<s.size();i++){
            if(s[i]=='(') left.push(i);
            else if(s[i]=='*') star.push(i);
            else {
                if(left.empty() && star.empty()) return false;
                if(!left.empty()) left.pop();
                else 
                    star.pop();
            }
        }
        while(!left.empty()&&!star.empty()){
            if(left.top()>star.top)return false;
            left.pop();
            star.pop();
        }
        return left.empty();
    }
}