max_stack_element.h

#ifndef CPP_ALGORITHM_MAX_STACK_ELEMENT_H
#define CPP_ALGORITHM_MAX_STACK_ELEMENT_H

#include <stack>
#include <stdexcept>

namespace MaxStackElement
{
 /**
 * \brief Custom stack that stores the maximum element.
 */
 class Stack
 {
 public:
 bool Empty() const { return std::empty(element_with_cached_max_); }

 int Max() const
 {
 if (Empty())
 {
 throw std::length_error("Empty stack!");
 }
 return element_with_cached_max_.top().max;
 }

 int Pop()
 {
 if (Empty())
 {
 throw std::length_error("Empty stack!");
 }
 const int pop_element = element_with_cached_max_.top().element;
 element_with_cached_max_.pop();
 return pop_element;
 }

 void Push(const int x)
 {
 element_with_cached_max_.emplace(ElementWithCachedMax{x, std::max(x, Empty() ? x : Max())});
 }

 private:
 struct ElementWithCachedMax
 {
 int element;
 int max;
 };

 /**
 * \brief Caches the maximum element in the stack.
 * \details Caches the maximum among the elements below the current element.
 */
 std::stack<ElementWithCachedMax> element_with_cached_max_;
 };
}

#endif