Check for Balanced Brackets in an expression (well-formedness) using Stack · Declare a character stack S.

BalancedBrackets.java

import java.io.*;
import java.math.*;
import java.security.*;
import java.text.*;
import java.util.*;
import java.util.concurrent.*;
import java.util.function.*;
import java.util.regex.*;
import java.util.stream.*;

import static java.util.stream.Collectors.joining;
import static java.util.stream.Collectors.toList;

class BalancedBracketsResult {

    /*
     * Complete the 'isBalanced' function below.
     *
     * The function is expected to return a STRING.
     * The function accepts STRING s as parameter.
     */

    public static String isBalanced(String s) {
        List<Character> stack = new ArrayList<>();

        for(int i=0;i<s.length();i++){
            System.out.println(stack.toString());
            if(s.charAt(i)=='{' || s.charAt(i)=='[' || s.charAt(i)=='('){
                stack.add(s.charAt(i));
            }
            if (stack.isEmpty())
                return "NO";

            char removed;
            switch (s.charAt(i)){
                case '}':
                    removed = stack.remove(stack.size()-1);
                    if(removed == '[' || removed == '(')
                        return "NO";
                    break;
                case ')':
                    removed = stack.remove(stack.size()-1);
                    if(removed == '[' || removed == '{')
                        return "NO";
                    break;
                case ']':
                    removed = stack.remove(stack.size()-1);
                    if(removed == '{' || removed == '(')
                        return "NO";
                    break;
            }
        }

        return (stack.isEmpty()) ? "YES" : "NO";
    }

}

public class BalancedBrackets {
    public static void main(String[] args) throws IOException {
        BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(System.in));
        BufferedWriter bufferedWriter = new BufferedWriter(new FileWriter(System.getenv("OUTPUT_PATH")));

        int t = Integer.parseInt(bufferedReader.readLine().trim());

        IntStream.range(0, t).forEach(tItr -> {
            try {
                String s = bufferedReader.readLine();

                String result = BalancedBracketsResult.isBalanced(s);

                bufferedWriter.write(result);
                bufferedWriter.newLine();
            } catch (IOException ex) {
                throw new RuntimeException(ex);
            }
        });

        bufferedReader.close();
        bufferedWriter.close();
    }
}