Question

Write Java code that prompts the user for a string and tells them if the grouping characters in that string are balanced. Grouping characters are ( and ), [ and ], and { and }. I got the basic idea for this problem from HackerRank. It’s also a very common interview question.

*******************8Example output**************

Enter the expression:{[()]} {[()]}

is balanced

Enter the expression: {()()} {()()}

is balanced

Enter the expression: {([[])} {([[])}

is not balanced

Enter the expression: {([)]} {([)]}

is not balanced

Answer 1

Iterate over each parantheses from start to end and do the below step at each iteration.

1. When you find opening bracket: will go Push.
2. When you find closing bracket: will go pop and check whether closing and opening bracket match.
3. If yes, then continue, if not then break and return NO.

import java.util.Arrays;

import java.util.List;

import java.util.Scanner;

import java.util.Stack;

public class Parantheses {

    

    public static void main(String args[]){

        Scanner sc = new Scanner(System.in); //enter the input expression

        System.out.print("Enter the expression:");

        String inputString = sc.nextLine();

        System.out.println(checkBraces(inputString));

        sc.close();

    }

    

    static String checkBraces(String v){

        Stack charstack = new Stack(); //instance of object creation

        String r = "is not balanced"; // initialization of variables

        char tmpChar;

        Character[] openingBraces = {'[','(','{'};

        Character[] closingBraces = {']',')','}'};

        List openingBracesList = Arrays.asList(openingBraces);

        List closingBracesList = Arrays.asList(closingBraces);

       

        

        

        if(v == null){

            return r;

        }else if(v.length()==0)

{ //v is value

            r = " is balanced";

        }else{

        

            for(int i=0; i < v.length(); i++) {

                tmpChar = v.charAt(i);

                

                if(openingBracesList.contains(tmpChar)){

                    charstack.push(tmpChar);

                }else if(closingBracesList.contains(tmpChar)){

                    if(!charstack.isEmpty()){

                        if(tmpChar==')' && '(' != charstack.pop()){

                            return r;

                        }else if(tmpChar=='}' && '{' !=charstack.pop()){ //poping character

                            return r;

                        }else if(tmpChar==']' && '[' != charstack.pop()){

                            return r;

                        }

                    }else{

                        return r;

                    }

                }else{

                    return r;

                }

            }

            

        }

        

        if( charstack.isEmpty()){

            r = " is balanced";

            return r;

        }else{

            return r;

        }

    }

}

output is: