leetcode-20-java

Given a string containing just the characters '(', ')', '{', '}', '[' and ']',
 determine if the input string is valid.

An input string is valid if:

Open brackets must be closed by the same type of brackets.
Open brackets must be closed in the correct order.
Note that an empty string is also considered valid.

    public static boolean isValid(String s) {
        if ("".equals(s)) {
            return true;
        }
        if (s.length()%2 != 0) {
            return false;
        }
        Stack<Character> stack = new Stack<>();
        char[] chars = s.toCharArray();
        for (char c : chars) {
            if (stack.isEmpty()) {
                stack.push(c);
                continue;
            }

            if (isMath(stack.peek(), c)) {
                stack.pop();
            } else {
                stack.push(c);
            }
        }

        return stack.isEmpty();
    }

    private static boolean isMath(char c1, char c2) {
//        if (c1 == '(') {
//            return c2 == ')';
//        } else if (c1 == '[') {
//            return c2 == ']';
//        } else if (c1 == '{') {
//            return c2 == '}';
//        }
        int sum = c1 + c2;
        return sum == 81 || sum == 184 || sum == 248;
    }