LRU cache solution

Author: Vadym Fedorov

lru-cache/solution_test.go

@@ -0,0 +1,85 @@
+package solution
+
+// Source: https://girai.dev/blog/lru-cache-implementation-in-go/
+
+import (
+	"container/list"
+	"testing"
+)
+
+type LRUCache struct {
+	cap int                   // capacity
+	l   *list.List            // doubly linked list
+	m   map[int]*list.Element // hash table for checking if list node exists
+}
+
+// Pair is the value of a list node.
+type ListItem struct {
+	key   int
+	value int
+}
+
+// Constructor initializes a new LRUCache.
+func Constructor(capacity int) LRUCache {
+	return LRUCache{
+		cap: capacity,
+		l:   new(list.List),
+		m:   make(map[int]*list.Element, capacity),
+	}
+}
+
+// Get a list node from the hash map.
+func (c *LRUCache) Get(key int) int {
+	// check if list node exists
+	node, ok := c.m[key]
+	if !ok {
+		return -1
+	}
+	c.l.MoveToFront(node)
+	return node.Value.(*list.Element).Value.(ListItem).value
+}
+
+// Put key and value in the LRUCache
+func (c *LRUCache) Put(key int, value int) {
+	// check if list node exists
+	if node, ok := c.m[key]; ok {
+		// move the node to front
+		c.l.MoveToFront(node)
+		// update the value of a list node
+		node.Value.(*list.Element).Value = ListItem{key: key, value: value}
+	} else {
+		// delete the last list node if the list is full
+		if c.l.Len() == c.cap {
+			// get the key that we want to delete
+			idx := c.l.Back().Value.(*list.Element).Value.(ListItem).key
+			// delete the node pointer in the hash map by key
+			delete(c.m, idx)
+			// remove the last list node
+			c.l.Remove(c.l.Back())
+		}
+		// initialize a list node
+		node := &list.Element{
+			Value: ListItem{
+				key:   key,
+				value: value,
+			},
+		}
+		// push the new list node into the list
+		ptr := c.l.PushFront(node)
+		// save the node pointer in the hash map
+		c.m[key] = ptr
+	}
+}
+
+func TestLRUCache(t *testing.T) {
+	cache := Constructor(2)
+	cache.Put(1, 1)
+	cache.Put(2, 2)
+	cache.Get(1)    // returns 1
+	cache.Put(3, 3) // evicts key 2
+	cache.Get(2)    // returns -1 (not found)
+	cache.Put(4, 4) // evicts key 1
+	cache.Get(1)    // returns -1 (not found)
+	cache.Get(3)    // returns 3
+	cache.Get(4)    // returns 4
+}