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) {
        Stack<Character> stack = new Stack<>();
        // write code here
        if (s == null || s.length() < 2) {
            return false;
        }

        char[] chars = s.toCharArray();
        for (int i = 0; i < chars.length; i++) {
		  // 成对则弹出
            if (chars[i] == ')') {
                if (stack.isEmpty() || stack.pop() != '(') {
                    return false;
                }
            } else if (chars[i] == '}') {
                if (stack.isEmpty() || stack.pop() != '{') {
                    return false;
                }
            } else if (chars[i] == ']') {
                if (stack.isEmpty() || stack.pop() != '[') {
                    return false;
                }
            } else {
                stack.push(chars[i]);
            }
        }
        
	  // 只有栈为空，才说明成对出现  
        return  stack.isEmpty();
    }
}