Container Adapters: stack, queue, priority_queue

Three adapters wrap a container and expose exactly one discipline. They are not containers themselves — you cannot iterate a stack.

#include <stack>
#include <queue>

std::stack<int> s;   // LIFO: push, pop, top          (defaults to deque)
std::queue<int> q;   // FIFO: push, pop, front, back  (defaults to deque)

#include <queue>
std::priority_queue<int> pq;  // largest pops first by default

priority_queue is a heap facade, not a sorted list: push is O(log n), top is O(1), but there is no iteration and no "update" — you push and pop.

A min-heap is spelled with the comparator form:

#include <vector>
#include <queue>
#include <functional>

std::priority_queue<int, std::vector<int>, std::greater<int>> min_heap;

When the ordering key is part of the value, give the element an operator< (or pass a comparator) — the adapter then ranks whole objects. That is exactly the mechanism Module 4's operator overloading feeds into.