LeetCode20. 有效的括号

class Solution {
    public boolean isValid(String s) {
        if (s == null || s.length() == 0) return true;
        /**
         * 解法1：
         */
        /*Stack<Character> stack = new Stack<>();
        for (int i = 0; i < s.length(); i++) {
            char c = s.charAt(i);
            if (c == ‘(‘ || c == ‘{‘ || c == ‘[‘) {
                stack.push(c);
            }else {
                if (stack.isEmpty()) {
                    return false;
                }
                char temp = stack.pop();
                if (c == ‘)‘ && temp != ‘(‘) return false;
                if (c == ‘}‘ && temp != ‘{‘) return false;
                if (c == ‘]‘ && temp != ‘[‘) return false;
            }
        }
        return stack.isEmpty();*/
        /**
         * 解法2：
         */
        Stack<Character> 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() || c != stack.pop()) {
                return false;
            }
        }
        return stack.isEmpty();
    }
}