stack_using_queue.cpp

 
#include <cassert>   
#include <cstdint>
#include <iostream>  
#include <queue>     
 
namespace data_structures {
namespace stack_using_queue {
struct Stack {
    std::queue<int64_t> main_q;       
    std::queue<int64_t> auxiliary_q;  
    uint32_t current_size = 0;        
 
    int top() { return main_q.front(); }
 
    void push(int val) {
        auxiliary_q.push(val);
        while (!main_q.empty()) {
            auxiliary_q.push(main_q.front());
            main_q.pop();
        }
        swap(main_q, auxiliary_q);
        current_size++;
    }
 
    void pop() {
        if (main_q.empty()) {
            return;
        }
        main_q.pop();
        current_size--;
    }
 
    int size() { return current_size; }
};
}  // namespace stack_using_queue
}  // namespace data_structures
 
static void test() {
    data_structures::stack_using_queue::Stack s;
    s.push(1);  
    s.push(2);  
    s.push(3);  
 
    assert(s.size() == 3);  
 
    assert(s.top() == 3);  
 
    s.pop();               
    assert(s.top() == 2);  
 
    s.pop();  
    assert(s.top() == 1);
 
    s.push(5);             
    assert(s.top() == 5);  
 
    s.pop();               
    assert(s.top() == 1);  
 
    assert(s.size() == 1);  
}
 
int main() {
    test();  // run self-test implementations
    return 0;
}