Demo.java

/*
Copyright (C) Deepali Srivastava - All Rights Reserved
This code is part of DSA course available on CourseGalaxy.com    
*/

package parentheses;
import java.util.Scanner;

public class Demo 
{
	public static void main(String[] args) 
	{
	  String expression;

	  Scanner scan = new Scanner(System.in);	
	  
	  System.out.print("Enter an expression with parentheses : ");
	  expression = scan.nextLine();
		
	  if(isValid(expression))
		  System.out.println("Valid expression");
	  else
		  System.out.println("Invalid expression");
	  scan.close();
     }
	
	
	  public static boolean isValid(String expr)
	  {
	  	StackA st = new StackA();

	  	char ch;
	  	for(int i=0; i<expr.length(); i++)
	  	{
	  		if(expr.charAt(i)=='(' || expr.charAt(i)=='{' || expr.charAt(i)=='[')
	  			st.push(expr.charAt(i));

	  		if(expr.charAt(i)==')' || expr.charAt(i)=='}' || expr.charAt(i)==']')
	  			if(st.isEmpty())    
	  			{
	  				System.out.println("Right parentheses are more than left parentheses");
	  				return false;
	  			}
	  			else
	  			{
	  				ch=st.pop();
	  				if(!matchParentheses(ch,expr.charAt(i))) 
	  				{
	  					System.out.println("Mismatched parentheses are : "); 
	  					System.out.println(ch + " and " + expr.charAt(i));	
	  					return false;
	  				}
	  			}
	  	}

	  	if(st.isEmpty()) 
	  	{
	  		System.out.println("Balanced Parentheses"); 
	  		return true;
	  	}
	  	else 
	  	{
	  		System.out.println("Left parentheses are more than right parentheses");	
	  		return false;
	  	}
	  	
	  }

	  public static boolean matchParentheses(char leftPar,char rightPar)
	  {
	  	if(leftPar=='[' && rightPar==']')
	  		return true;
	  	if(leftPar=='{' && rightPar=='}')
	  		return true;	
	  	if(leftPar=='(' && rightPar==')')
	  		return true;
	  	return false;
	  }
}