ZA | 25-SDC-July | Luke Manyamazi | Sprint 2 | Implement LRU Cache

Sprint-2/implement_lru_cache/lru_cache.py

@@ -0,0 +1,35 @@
+class LruCache:
+    def __init__(self, limit):
+        if limit <= 0:
+            raise ValueError("Limit must be greater than 0")
+
+        self.limit = limit
+        self.cache = {}
+        self.access_order = []  # most recent at the end
+
+    def get(self, key):
+        if key in self.cache:
+            # Move to most recent position
+            self.access_order.remove(key)
+            self.access_order.append(key)
+            return self.cache[key]
+        return None
+
+    def set(self, key, value):
+        if key in self.cache:
+            # Update existing key
+            self.cache[key] = value
+            # Move to most recent position  
+            self.access_order.remove(key)
+            self.access_order.append(key)
+        else:
+            # New key
+            if len(self.cache) >= self.limit:
+                # Remove least recently used (first item)
+                lru_key = self.access_order[0]
+                del self.cache[lru_key]
+                self.access_order.pop(0)
+
+            # Add new key as most recent
+            self.cache[key] = value
+            self.access_order.append(key)

Sprint-2/implement_lru_cache/lru_cache_test.py

@@ -54,6 +54,46 @@ def test_eviction_order_after_gets(self):
         self.assertEqual(cache.get("a"), 1)
         self.assertEqual(cache.get("c"), 3)
 
+    def test_get_refreshes_item(self):
+        """Test that getting an item makes it recently used"""
+        cache = LruCache(limit=2)
+
+        cache.set("a", 1)
+        cache.set("b", 2)
+
+        # Access "a" to make it recently used
+        cache.get("a")
+
+        # Add new item - should evict "b" not "a"
+        cache.set("c", 3)
+
+        self.assertIsNone(cache.get("b"))  # "b" was evicted
+        self.assertEqual(cache.get("a"), 1)  # "a" remains
+        self.assertEqual(cache.get("c"), 3)
+
+    def test_complex_usage_pattern(self):
+        """Test LRU behavior with multiple operations"""
+        cache = LruCache(limit=3)
+
+        # Add initial items
+        cache.set("a", 1)
+        cache.set("b", 2)
+        cache.set("c", 3)
+
+        # Use items in various order
+        cache.get("a")
+        cache.get("c") 
+        cache.get("b")
+        cache.get("a")
+
+        # Add new item - should evict least recently used ("c")
+        cache.set("d", 4)
+
+        self.assertIsNone(cache.get("c"))  # "c" was evicted
+        self.assertEqual(cache.get("a"), 1)
+        self.assertEqual(cache.get("b"), 2)
+        self.assertEqual(cache.get("d"), 4)
+
 
 if __name__ == "__main__":
     unittest.main()