Title 20, effective brackets

I, entitled ¹

Second, the idea

The establishment of a stack, when traversed all left parenthesis are pushed onto the stack, there is a time right parenthesis appears on top of the stack brackets and determine the current right parenthesis is not a right, yes, then it will pop, or returns false.

When judged as a character input only occurs in "() {} []" of these types, and between two brackets ASCii pairing value greater than zero is less than 3, it can be directly used as the determination condition.

Third, the code

import java.util.ArrayList;
import java.util.List;

public class T0020 {

    public static void main(String[] args) {

        System.out.println( isValid("[") );            //true
        System.out.println( isValid("()[]{}") );        //true
        System.out.println( isValid("(]") );            //false
        System.out.println( isValid("([)]") );          //false
        System.out.println( isValid("{[]}") );          //true
        System.out.println( isValid("{{)}") );          //false

    }

    public static boolean isValid(String s) {

        List<Integer> stoke = new ArrayList<Integer>();     //存储还未配对的括号，用于判断

        //对字符串进行遍历
        for ( char i : s.toCharArray() ){
            
            //如果是左括号就将其压入栈中，右括号就进行对应的处理
            if ( i == '(' || i == '{' || i == '[' ){
                stoke.add( (int)i );
            }else {
                
                //如果栈中已经空了，就返回false
                if (stoke.size() == 0 )
                    return false;

                //栈中存储的括号能和当前括号配对就将其出栈，否则返回false
                if ( ((int)i - stoke.get(stoke.size()-1)) < 3 && ((int)i - stoke.get(stoke.size()-1)) > 0 ){
                    stoke.remove(stoke.size()-1);
                }else
                    return false;
            }
        }

        //只有栈中已经空了才返回true
        return stoke.size()==0;
    }
}

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1. Source: stay button (LeetCode)
   link: https: //leetcode-cn.com/problems/valid-parentheses
   copyrighted by deduction from all networks. Commercial reprint please contact the authorized official, non-commercial reprint please indicate the source. ↩︎