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
        Stack<String> stack = new Stack<>();
        for(int i = 0;i<s.length();i++){
            String s2 = s.substring(i,i+1);
            if(s2.equals("(")||s2.equals("{")||s2.equals("[")){
                stack.push(s2);
            }else{
                if(stack.isEmpty()){
                    return false;
                }
                String s1 = stack.pop();
                
                if(s2.equals(")")&&!s1.equals("(")){
                    return false;
                }
                if(s2.equals("}")&&!s1.equals("{")){
                    return false;
                }
                if(s2.equals("]")&&!s1.equals("[")){
                    return false;
                }
            }
        }
        if(!stack.isEmpty()){
            return false;
        }
        return true;
    }
}