题解 | 有效括号序列

import java.util.*;


public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param s string字符串 
     * @return bool布尔型
     */
    public boolean isValid (String s) {
        // write code here
        java.util.Stack stack  = new java.util.Stack();
        for(int i=0;i<s.length();i++) {
            char ch = s.charAt(i);
            if (ch == '(' || ch == '{' || ch == '[') {
                stack.add(ch);
            } else {
                if (stack.isEmpty()) {
                    return false;
                }
                char p = (char)stack.peek();
                boolean match = ((p == '(' && ch == ')') || (p == '{' && ch == '}') || (p == '[' && ch == ']'));
                if (match) stack.pop();
                else return false;
            }
        }

        return stack.isEmpty();
    }
}