#include<assert.h>

template<class T>

class queue

{

struct listnode {

listnode* next;

T value;

listnode(listnode* node, T v): next(node), value(v) {}

};

public:

queue(): begin(nullptr), end(nullptr), size(0) {}

~queue()

{

while (begin != nullptr)

{

listnode* temp = begin;

begin = begin->next;

delete temp;

}

}

void enqueue(const T& value)

{

if (size == 0)

{

begin = new listnode(nullptr, value);

end = begin;

}

else

{

end->next = new listnode(nullptr, value);

end = end->next;

}

size++;

}

void dequeue()

{

assert(size > 0);

listnode* temp = begin;

begin = begin->next;

delete temp;

size--;

}

T front()

{

return begin->value;

}

int length()

{

return size;

}

private:

listnode* begin;

listnode* end;

int size;

};