题解 | #有效括号序列#

import java.util.*;


public class Solution {
    /**
     * 
     * @param s string字符串 
     * @return bool布尔型
     */
    public boolean isValid (String s) {
        // write code here
        if (s == null || s.length() < 2) {
            return false;
        }
        char[] arr = s.toCharArray();
        Stack<Character> stack = new Stack<>();
        for (int i = 0; i < arr.length; i++) {
            if (!stack.isEmpty() && ((stack.peek() == '(' && arr[i] == ')') 
                || (stack.peek() == '[' && arr[i] == ']')
                || (stack.peek() == '{' && arr[i] == '}'))) {
                stack.pop();
            } else {
                stack.push(arr[i]);
            }
        }
        return stack.isEmpty();
    }
}