题解 | #有效括号序列#

比较简单也没有太多技巧。用栈即可

import java.util.*;


public class Solution {
    /**
     * 
     * @param s string字符串 
     * @return bool布尔型
     */
    public boolean isValid (String s) {
        if (s == null) {
            return false;
        }
        // write code here
        Stack<Character> stack = new Stack();
        for(int i = 0; i < s.length(); i++) {
            switch(s.charAt(i)) {
                case '(':
                case '{':
                case '[':
                    stack.push(s.charAt(i));
                    break;
                case ')':
                    if (stack.isEmpty() || stack.pop() != '(') {
                        return false;
                    }
                    break;
                 case '}':
                    if (stack.isEmpty() || stack.pop() != '{') {
                        return false;
                    }
                    break;
                case ']':
                    if (stack.isEmpty() || stack.pop() != '[') {
                        return false;
                    }
                    break;
                default: return false;
            }
        }
        return stack.isEmpty();
    }
}