Checking nested parentheses

Author: Deepali-Srivastava

stack/parentheses/Demo.java

@@ -0,0 +1,79 @@
+/*
+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;
+	  }
+}

stack/parentheses/StackA.java

@@ -0,0 +1,94 @@
+/*
+Copyright (C) Deepali Srivastava - All Rights Reserved
+This code is part of DSA course available on CourseGalaxy.com    
+*/
+
+package parentheses;
+
+import java.util.EmptyStackException;
+
+public class StackA 
+{
+    private char[] stackArray;
+    private int top;
+	
+    public StackA()
+    {
+       	stackArray = new char[10];
+    	top = -1;
+    }
+    
+    public StackA(int maxSize)
+    {
+    	stackArray = new char[maxSize];
+    	top=-1;
+    }
+    public int size()
+    {
+    	return top+1;
+    }
+
+    public boolean isEmpty()
+    {
+    	return (top==-1);
+    }
+
+    public boolean isFull()
+    {
+    	return (top==stackArray.length-1);
+    }
+
+    public void push(char x)
+    {
+    	if(isFull())
+    	{
+    		System.out.println("Stack Overflow\n");
+    		return;
+    	}
+    	top=top+1;
+    	stackArray[top]=x;
+    }
+
+    public char pop()
+    {
+    	char x;
+    	if(isEmpty())
+    	{
+    		System.out.println("Stack Underflow\n");
+    		throw new EmptyStackException();
+    	}
+    	x=stackArray[top];
+    	top=top-1;
+    	return x;
+    }
+
+    public char peek()
+    {
+    	if(isEmpty())
+    	{
+    		System.out.println("Stack Underflow\n");
+    		throw new EmptyStackException();
+    	}
+    	return stackArray[top];
+    }
+
+
+    public void display()
+    {
+    	int i;
+    	
+    	System.out.println("top= " + top);
+
+    	if(isEmpty())
+    	{
+    		System.out.println("Stack is empty");
+    		return;
+    	}
+        System.out.println("Stack is : ");
+    	for(i=top; i>=0; i--)
+    		System.out.println(stackArray[i] + " ");
+    	System.out.println();
+    }
+
+
+}