import java.util.*;

/**
 * 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.
 *
 * Approach: Save min of previous state before pushing new minimum value. Therefore we can ste the minimum of the previous state in O(1) time.
 * Time complexity of every method: O(1)
 * Space complexity: O(n)
 */
class MinStack {
    int min;
    Stack<Integer> stack;

    public MinStack() {
        stack = new Stack<>();
        min = Integer.MAX_VALUE;
    }

    public void push(int x) {
        if (x <= min) {
            stack.push(min);
            min = x;
        }
        stack.push(x);
    }

    public void pop() {
        if (stack.pop() == min) {
            min = stack.pop();
        }
    }

    public int top() {
        if (stack.size() == 0) return Integer.MAX_VALUE;
        return stack.peek();
    }

    public int getMin() {
        return min;
    }

}



