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import std.array : appender;
private struct Node(T) {
Node!T* prev;
Node!T* next;
T data;
}
private struct List(T) {
Node!T* head;
Node!T* tail;
size_t length;
invariant () {
if (length > 0) {
assert(head !is null);
assert(tail !is null);
}
}
/*private void check()
{
Node!T* cur = head;
while (true)
{
if (cur != head)
assert(cur.prev);
if (cur == tail)
break;
else
assert(cur.next);
cur = cur.next;
}
}*/
void remove(Node!T* n) {
if (n.next)
n.next.prev = n.prev;
if (n.prev)
n.prev.next = n.next;
if (head == n)
head = head.next;
if (tail == n)
tail = tail.prev;
length--;
}
void push(Node!T* n) {
n.prev = null;
n.next = head;
head = n;
if (tail is null)
tail = head;
else
head.next.prev = head;
length++;
}
Node!T* pop()
in {
assert(tail);
}
do {
Node!T* node = tail;
remove(node);
return node;
}
}
unittest {
List!int l;
Node!int first;
l.push(&first);
assert(l.head == &first);
assert(l.tail == &first);
Node!int second;
l.push(&second);
assert(l.head == &second);
assert(l.tail == &first);
assert(l.pop() == &first);
assert(l.head == &second);
assert(l.tail == &second);
l.push(&first);
l.pop();
l.pop();
}
class LRUCache(From, To) {
private size_t _cap;
private struct Record {
To val;
From key;
}
private Node!Record*[From] map;
private List!Record queue;
this(size_t cap) {
_cap = cap;
}
private void checksz() {
if (queue.length > _cap) {
auto node = queue.pop();
map.remove(node.data.key);
}
}
bool opBinaryRight(string op : "in")(From key) {
return cast(bool)(key in map);
}
To opIndex(From f)
in {
assert(f in map);
}
do {
auto p = map[f];
queue.remove(p);
queue.push(p);
return p.data.val;
}
void opIndexAssign(To t, From f) {
auto p = f in map;
Node!Record* node;
bool alloc = p is null;
if (!alloc) {
queue.remove(*p);
node = *p;
} else
node = new Node!Record();
node.data.val = t;
node.data.key = f;
queue.push(node);
map[f] = node;
if (alloc)
checksz();
}
}
unittest {
auto cache = new LRUCache!(int, int)(2);
cache[0] = 1;
cache[4] = 2;
cache[5] = 1;
assert(0 !in cache);
assert(4 in cache);
assert(5 in cache);
assert(cache[5] == 1); // prioritizes
cache[0] = 1;
assert(4 !in cache);
}
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