test: add examples for lrucache

algorithm/lrucache.go

@@ -0,0 +1,121 @@
+package algorithm
+
+type lruNode[K comparable, V any] struct {
+	key   K
+	value V
+	pre   *lruNode[K, V]
+	next  *lruNode[K, V]
+}
+
+// newLruNode return a lruNode pointer
+func newLruNode[K comparable, V any](key K, value V) *lruNode[K, V] {
+	return &lruNode[K, V]{
+		key:   key,
+		value: value,
+		pre:   nil,
+		next:  nil,
+	}
+}
+
+// LRUCache lru cache (thread unsafe)
+type LRUCache[K comparable, V any] struct {
+	cache    map[K]*lruNode[K, V]
+	head     *lruNode[K, V]
+	tail     *lruNode[K, V]
+	capacity int
+	length   int
+}
+
+// NewLRUCache creates a LRUCache pointer instance.
+func NewLRUCache[K comparable, V any](capacity int) *LRUCache[K, V] {
+	return &LRUCache[K, V]{
+		cache:    make(map[K]*lruNode[K, V], capacity),
+		head:     nil,
+		tail:     nil,
+		capacity: capacity,
+		length:   0,
+	}
+}
+
+// Get value of key from lru cache.
+// Play: https://go.dev/play/p/iUynEfOP8G0
+func (l *LRUCache[K, V]) Get(key K) (V, bool) {
+	var value V
+
+	node, ok := l.cache[key]
+	if ok {
+		l.moveToHead(node)
+		return node.value, true
+	}
+
+	return value, false
+}
+
+// Put value of key into lru cache.
+// Play: https://go.dev/play/p/iUynEfOP8G0
+func (l *LRUCache[K, V]) Put(key K, value V) {
+	node, ok := l.cache[key]
+	if !ok {
+		newNode := newLruNode(key, value)
+		l.cache[key] = newNode
+		l.addNode(newNode)
+
+		if len(l.cache) > l.capacity {
+			oldKey := l.deleteNode(l.head)
+			delete(l.cache, oldKey)
+		}
+	} else {
+		node.value = value
+		l.moveToHead(node)
+	}
+	l.length = len(l.cache)
+}
+
+// Delete item from lru cache.
+func (l *LRUCache[K, V]) Delete(key K) bool {
+	node, ok := l.cache[key]
+	if ok {
+		key := l.deleteNode(node)
+		delete(l.cache, key)
+		return true
+	}
+
+	return false
+}
+
+// Len returns the number of items in the cache.
+func (l *LRUCache[K, V]) Len() int {
+	return l.length
+}
+
+func (l *LRUCache[K, V]) addNode(node *lruNode[K, V]) {
+	if l.tail != nil {
+		l.tail.next = node
+		node.pre = l.tail
+		node.next = nil
+	}
+	l.tail = node
+	if l.head == nil {
+		l.head = node
+	}
+}
+
+func (l *LRUCache[K, V]) deleteNode(node *lruNode[K, V]) K {
+	if node == l.tail {
+		l.tail = l.tail.pre
+	} else if node == l.head {
+		l.head = l.head.next
+	} else {
+		node.pre.next = node.next
+		node.next.pre = node.pre
+	}
+	return node.key
+}
+
+func (l *LRUCache[K, V]) moveToHead(node *lruNode[K, V]) {
+	if l.tail == node {
+		return
+	}
+	l.deleteNode(node)
+	l.addNode(node)
+}