diff --git a/src/leetcode/design.md b/src/leetcode/design.md
index f936956..245b503 100644
--- a/src/leetcode/design.md
+++ b/src/leetcode/design.md
@@ -1 +1,42 @@
-# Design
\ No newline at end of file
+# Design
+
++ [LRU Cache](#lru-cache)
+
+## LRU Cache
+https://leetcode.com/problems/lru-cache/
+```java
+class LRUCache {
+    private final LinkedHashMap<Integer, Integer> cache = new LinkedHashMap<>();
+    private final int capacity;
+    public LRUCache(int capacity) {
+        this.capacity = capacity;
+    }
+
+    public int get(int key) {
+        if (!cache.containsKey(key)) {
+            return -1;
+        }
+        update(key);
+        return cache.get(key);
+    }
+
+    public void put(int key, int value) {
+        if (cache.containsKey(key)) {
+            cache.put(key, value);
+            update(key);
+            return;
+        }
+        if (cache.size() >= this.capacity) {
+            int del = cache.keySet().iterator().next();
+            cache.remove(del);
+        }
+        cache.put(key, value);
+    }
+    public void update(int key) {
+        int val = cache.get(key);
+        cache.remove(key);
+        cache.put(key, val);
+    }
+}
+
+```
\ No newline at end of file