Min Stack Java

Design a stack that supports push, pop, top, and retrieving the minimum element in constant time.

push(x) -- Push element x onto stack.

pop() -- Removes the element on top of the stack.

top() -- Get the top element.

getMin() -- Retrieve the minimum element in the stack.

Example:

MinStack minStack = new MinStack(); minStack.push(-2); minStack.push(0); minStack.push(-3); minStack.getMin(); --> Returns -3. minStack.pop(); minStack.top(); --> Returns 0. minStack.getMin(); --> Returns -2. 

Hint: Consider each node in the stack having a minimum value.

Include a lot of code comments in your source code. I don't understand the logic behind push(int x), pop() , top(), and getMin(). I know the hint told us to consider each node in the stack having a minimum value, but I am still confused.?

Source Code

//A class Element that has data and minimum

class Element {

public int data;

public int minimum;

public Element next;

public Element(int value, int minimum) {

this.data = value;

this.minimum = minimum;

}

}

//Our class MinStack

public class MinStack {

//Top element of Stack of Type element

public Element top;

public MinStack() {

}

//Push element at Top of stack and keep minimum in minimum

public void push(int x) {

if (top == null) {

top = new Element(x, x);

} else {

Element e = new Element(x, Math.min(x, top.minimum));

e.next = top;

top = e;

}

}

public void pop() {

if (top == null)

return;

Element temp = top.next;

top.next = null;

top = temp;

}

public int top() {

if (top == null)

return -1;

return top.data;

}

public int getMin() {

if (top == null)

return -1;

return top.minimum;

}

public static void main(String[] args) {

MinStack minStack = new MinStack();

minStack.push(-2);

minStack.push(0);

minStack.push(-3);

System.out.println(minStack.getMin()); // --> Returns -3.

minStack.pop();

System.out.println(minStack.top()); // --> Returns 0.

System.out.println(minStack.getMin()); // --> Returns -2.

}

}