Design a stack to support push, pop, and retrieving the minimum?

element in constant time

public class MinStack {

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

private Stack<int> minStack = new Stack<int>();

Follow on:

public void Push(int x) {

stack.Push(x);

if (minStack.Count == 0 || x <= minStack.Peek())

minStack.Push(x);

public void Pop() {

if (stack.Peek() == minStack.Peek())

minStack.Pop();

stack.Pop();

public int Top() {

return stack.Peek();

public int GetMin() {

return minStack.Peek();

Explanation:

Use two stacks: one normal stack, one for minimum values. When pushing a smaller or

equal value, push it on minStack; when popping, pop minStack if needed.