Question

Write a Java program which takes a String representing an arithmetic expression as an input and displays whether or not the expression is balanced. If the expression is not balanced (i.e. the wrong # of parentheses or in the wrong order) it will display an error message. For Example: Input an expression: ( ( 2 + 4 ) * 2 ) Expression is balanced Input an expression: ( 5 * 7 – 6 ) ) Error: Expression is not balanced.... Implement a stack calculator using both a numbers and operations stack. Be sure to check that the expression is balanced before running it through the calculator.

Answer 1

import java.util.*;
import java.io.*;
public class Main
   {
                public static void main(String[] args) {
                 Scanner sc= new Scanner(System.in); //System.in is a standard input stream.
             System.out.print("Enter arthematic expression: ");
             String str= sc.nextLine(); //reads string.
             String result=check(str);
             System.out.print(str+" is "+result);
        
            }
             public static String check(String expr)
             {
             if (expr.isEmpty())
             return "Balanced";
             
             Stack<Character> stack = new Stack<Character>();
             for (int i = 0; i < expr.length(); i++)
               {
                     char current = expr.charAt(i);
                     if (current == '{' || current == '(' || current == '[')
                     {
                         stack.push(current);
                     }
                     if (current == '}' || current == ')' || current == ']')
                     {
                         if (stack.isEmpty())
                         return "Not Balanced";
                         char last = stack.peek();
                         if (current == '}' && last == '{' || current == ')' && last == '(' || current == ']' && last == '[')
                         stack.pop();
                         else 
                         return "Not Balanced";
                     }
                }
             return stack.isEmpty()?"Balanced":"Not Balanced";
             }
                
}