add LRU Cache

lru/coverage.out

@@ -0,0 +1,24 @@
+mode: set
+github.com/cubixle/lru/lru.go:11.31,17.2 1 1
+github.com/cubixle/lru/lru.go:19.40,21.9 2 1
+github.com/cubixle/lru/lru.go:21.9,23.3 1 0
+github.com/cubixle/lru/lru.go:25.2,25.14 1 1
+github.com/cubixle/lru/lru.go:25.14,27.3 1 0
+github.com/cubixle/lru/lru.go:29.2,29.15 1 1
+github.com/cubixle/lru/lru.go:32.38,34.9 2 1
+github.com/cubixle/lru/lru.go:34.9,39.23 3 1
+github.com/cubixle/lru/lru.go:39.23,46.4 4 1
+github.com/cubixle/lru/lru.go:48.3,48.9 1 1
+github.com/cubixle/lru/lru.go:51.2,52.23 2 0
+github.com/cubixle/lru/lru.go:68.22,70.2 1 1
+github.com/cubixle/lru/lru.go:72.37,73.19 1 1
+github.com/cubixle/lru/lru.go:73.19,78.3 3 1
+github.com/cubixle/lru/lru.go:80.2,85.39 5 1
+github.com/cubixle/lru/lru.go:88.50,97.2 3 1
+github.com/cubixle/lru/lru.go:99.32,100.14 1 1
+github.com/cubixle/lru/lru.go:100.14,102.3 1 0
+github.com/cubixle/lru/lru.go:104.2,108.17 4 1
+github.com/cubixle/lru/lru.go:108.17,110.3 1 0
+github.com/cubixle/lru/lru.go:113.29,116.2 2 1
+github.com/cubixle/lru/lru.go:118.24,120.18 2 1
+github.com/cubixle/lru/lru.go:120.18,123.3 2 1

lru/go.mod

@@ -0,0 +1,3 @@
+module github.com/cubixle/lru
+
+go 1.21.6

lru/lru.go

@@ -0,0 +1,121 @@
+package lru
+
+import "log"
+
+type Cache struct {
+	cap int
+	m   map[string]*node
+	l   *list
+}
+
+func NewCache(cap int) *Cache {
+	return &Cache{
+		cap: cap,
+		m:   make(map[string]*node, 2),
+		l:   newList(),
+	}
+}
+
+func (c *Cache) Get(key string) string {
+	v, ok := c.m[key]
+	if !ok {
+		return ""
+	}
+
+	if v == nil {
+		return ""
+	}
+
+	return v.data
+}
+
+func (c *Cache) Set(key, val string) {
+	node, ok := c.m[key]
+	if !ok {
+		node := c.l.pushFront(key, val)
+
+		c.m[key] = node
+
+		if len(c.m) > c.cap {
+			n := c.l.back()
+			c.l.remove(n)
+			delete(c.m, n.key)
+		}
+
+		return
+	}
+
+	node.data = val
+	c.l.moveToFront(node)
+}
+
+type node struct {
+	key  string
+	data string
+	next *node
+	prev *node
+}
+
+type list struct {
+	head *node
+}
+
+func newList() *list {
+	return &list{}
+}
+
+func (l *list) moveToFront(n *node) {
+	if l.head == nil {
+		n.prev = l.head
+		l.head = n
+		l.head.prev = n
+	} else {
+		n.next = l.head
+		n.prev = l.head.prev
+		l.head.prev = n
+		l.head = n
+	}
+}
+
+func (l *list) pushFront(key, data string) *node {
+	n := &node{
+		key:  key,
+		data: data,
+	}
+
+	l.moveToFront(n)
+
+	return n
+}
+
+func (l *list) remove(n *node) {
+	if n == nil {
+		return
+	}
+
+	n.prev.next = n.next
+	if n.next != nil {
+		n.next.prev = n.prev
+	}
+
+	n = nil
+}
+
+func (l *list) back() *node {
+	return l.head.prev
+}
+
+func (l *list) debug() {
+	log.Println("--------")
+	start := l.head.data
+	node := l.head
+	for node != nil {
+		log.Println(node)
+
+		node = node.next
+		if node != nil && node.data == start {
+			break
+		}
+	}
+	log.Println("--------")
+}

lru/lru_test.go

@@ -0,0 +1,35 @@
+package lru_test
+
+import (
+	"testing"
+
+	"github.com/cubixle/lru"
+)
+
+func TestCache(t *testing.T) {
+	cache := lru.NewCache(2)
+	cache.Set("usa", "washington")
+	cache.Set("uk", "london")
+
+	city := cache.Get("usa")
+	if city != "washington" {
+		t.Fatal("didn't get the correct city for usa")
+	}
+
+	city = cache.Get("uk")
+	if city != "london" {
+		t.Fatal("didn't get the correct city for uk")
+	}
+
+	cache.Set("france", "paris")
+
+	city = cache.Get("france")
+	if city != "paris" {
+		t.Fatal("didn't get the correct city for uk")
+	}
+
+	city = cache.Get("usa")
+	if city != "" {
+		t.Fatal("usa is still in the cache but should have been removed")
+	}
+}