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package stack;

import java.util.Stack;

/**

* Created by gouthamvidyapradhan on 08/03/2017. Design a stack that supports push, pop, top, and

* retrieving the minimum element in constant time.

*

* <p>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.

*/

public class MinStack {

class Node {

int value, min;

Node(int value, int min) {

this.value = value;

this.min = min;

}

}

private Stack<Node> stack = new Stack<>();

/**

* Main method

*

* @param args

* @throws Exception

*/

public static void main(String[] args) throws Exception {

MinStack minStack = new MinStack();

minStack.push(-2);

minStack.push(0);

minStack.push(-3);

System.out.println(minStack.getMin());

minStack.pop();

System.out.println(minStack.top());

System.out.println(minStack.getMin());

}

public MinStack() {}

public void push(int x) {

Node node;

if (!stack.isEmpty()) {

Node top = stack.peek();

node = new Node(x, Math.min(top.min, x));

} else {

node = new Node(x, x);

}

stack.push(node);

}

public void pop() {

stack.pop();

}

public int top() {

return stack.peek().value;

}

public int getMin() {

return stack.peek().min;

}

}