Merge pull request #116 from vaskoz/day52

Day52

README.md

@@ -62,4 +62,5 @@ problems from
 * [Day 47](https://github.com/vaskoz/dailycodingproblem-go/issues/105)
 * [Day 49](https://github.com/vaskoz/dailycodingproblem-go/issues/107)
 * [Day 50](https://github.com/vaskoz/dailycodingproblem-go/issues/110)
+* [Day 52](https://github.com/vaskoz/dailycodingproblem-go/issues/113)
 * [Day 53](https://github.com/vaskoz/dailycodingproblem-go/issues/114)

day52/problem.go

@@ -0,0 +1,49 @@
+package day52
+
+import (
+	"container/list"
+)
+
+// Cache specifies a generic cache interface of key-value pairs.
+type Cache interface {
+	Set(key, value interface{})
+	Get(key interface{}) interface{}
+}
+
+type kvPair struct {
+	k, v interface{}
+}
+
+type lruCache struct {
+	data     map[interface{}]*list.Element
+	l        *list.List
+	capacity int
+}
+
+func (lc *lruCache) Set(key interface{}, value interface{}) {
+	if elem, found := lc.data[key]; found {
+		lc.l.MoveToFront(elem)
+		elem.Value = kvPair{k: key, v: value}
+		return
+	}
+	if len(lc.data) == lc.capacity { // evict oldest
+		oldest := lc.l.Back()
+		delete(lc.data, oldest.Value.(kvPair).k)
+		lc.l.Remove(oldest)
+	}
+	e := lc.l.PushFront(kvPair{k: key, v: value})
+	lc.data[key] = e
+}
+
+func (lc *lruCache) Get(key interface{}) interface{} {
+	if elem, found := lc.data[key]; found {
+		lc.l.MoveToFront(elem)
+		return elem.Value.(kvPair).v
+	}
+	return nil
+}
+
+// NewLRU returns a Cache implementation that behaves as a LRU.
+func NewLRU(capacity int) Cache {
+	return &lruCache{make(map[interface{}]*list.Element), list.New(), capacity}
+}

day52/problem_test.go

@@ -0,0 +1,49 @@
+package day52
+
+import "testing"
+
+func TestLRUCache(t *testing.T) {
+	lru := NewLRU(3)
+	for i := 0; i < 6; i++ {
+		lru.Set(i, i+1)
+	}
+	for i := 0; i < 3; i++ {
+		if v := lru.Get(i); v != nil {
+			t.Errorf("Expected these to be evicted")
+		}
+	}
+	for i := 3; i < 6; i++ {
+		if v := lru.Get(i); v != i+1 {
+			t.Errorf("Expected the values to remain")
+		}
+	}
+	for i := 3; i < 6; i++ {
+		lru.Set(i, 10*i)
+	}
+	for i := 3; i < 6; i++ {
+		if v := lru.Get(i); v != i*10 {
+			t.Errorf("Expected the values to modify")
+		}
+	}
+}
+
+func BenchmarkLRUCache(b *testing.B) {
+	lru := NewLRU(3)
+	for bm := 0; bm < b.N; bm++ {
+		for i := 0; i < 6; i++ {
+			lru.Set(i, i+1)
+		}
+		for i := 0; i < 3; i++ {
+			lru.Get(i)
+		}
+		for i := 3; i < 6; i++ {
+			lru.Get(i)
+		}
+		for i := 3; i < 6; i++ {
+			lru.Set(i, 10*i)
+		}
+		for i := 3; i < 6; i++ {
+			lru.Get(i)
+		}
+	}
+}