MinStack.java

package questions.virendra;

public class MinStack {
	
	Node top;
	
	public void push(int x)
	{
		if(top == null)
		{
			top = new Node(x);
		}
		else
		{
			Node temp = new Node(x);
			temp.next = top;
			temp.min = Math.min(top.min, x);
			top = temp;
		}
	}
	
	public void pop()
	{
		if(top == null)
		{
			System.out.println("Stack empty!");
			return;
		}
		
		top = top.next;
	}
	
	public int top()
	{
		if(top == null)
		{
			System.out.println("Stack empty!");
			return Integer.MAX_VALUE;
		}
		
		return top.value;
	}
	
	public int min()
	{
		if(top == null)
		{
			System.out.println("Stack empty!");
			return Integer.MAX_VALUE;
		}
		
		return top.min;
			
	}
	
	public static void main(String args[])
	{
		MinStack mStack = new MinStack();
		mStack.push(7);
		mStack.push(8);
		System.out.println(mStack.min());
		mStack.push(5);
		mStack.push(9);
		System.out.println(mStack.min());
		mStack.push(5);
		mStack.push(2);
		System.out.println(mStack.min());
		mStack.pop();
		mStack.pop();
		System.out.println(mStack.min());
	}
	
	
}

class Node {
	int value;
	int min;
	Node next;
	
	Node(int x)
	{
		value = x;
		next = null;
		min = x;
	}
}