题解 | #完成括号匹配#

import java.util.Scanner;
import java.util.Stack;

public class Main {
    public static void main(String[] args){
        Scanner in = new Scanner(System.in);

        while(in.hasNext()){
            solution(in);
        }
    }

    /**
     * 模拟法: 栈
     */
    private static void solution(Scanner in){
        String s = in.nextLine();

        Stack<Character> stack = new Stack<>();

        for(char ch: s.toCharArray()){
            if(ch == '['){
                stack.push(ch);
            }else{
                if(!stack.isEmpty()){
                    if(stack.peek() == '['){
                        stack.pop();
                    }else{
                        stack.push(ch);
                    }
                }else{
                    stack.push(ch);
                }
            }
        }

        StringBuilder sb = new StringBuilder(s);
        char top;
        while(!stack.isEmpty()){
            top = stack.pop();
            if(top == '['){
                sb.append(']');
            }else{
                sb.insert(0, '[');
            }
        }

        System.out.println(sb);
    }
}