[Day3]20. Valid Parentheses

Given a string containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.
The brackets must close in the correct order, "()" and "()[]{}" are all valid but "(]" and "([)]" are not.

No doubt, this problem is supposed to solve using 'stack'.
My solution takes 58 ms. And then, I found the top solution is really beautiful and only takes 9 ms! So…

public static boolean isValid(String s) {
    Stack stack = new Stack();
    for (int i = 0; i < s.length(); i++) {
        int n = 99;
        if (s.charAt(i) == '(')
            n = 1;
        if (s.charAt(i) == '[')
            n = 2;
        if (s.charAt(i) == '{')
            n = 3;
        if (s.charAt(i) == ')')
            n = -1;
        if (s.charAt(i) == ']')
            n = -2;
        if (s.charAt(i) == '}')
            n = -3;
        int lastone = 99;
        if (!stack.isEmpty())
            lastone = stack.lastElement();
        System.out.println(lastone);

        if (lastone + n == 0) {
            stack.pop();
        } else {
            stack.push(n);
        }
    }
    if (stack.isEmpty())
        return true;
    return false;
}

public static boolean isValidTop(String s) {
    Stack stack = new Stack();
    for (char c : s.toCharArray()) {
        if (c == '(')
            stack.push(')');
        else if (c == '{')
            stack.push('}');
        else if (c == '[')
            stack.push(']');
        else if (stack.isEmpty() || stack.pop() != c)
            return false;
    }
    return stack.isEmpty();
}