Add 014

Author: tobegit3hub

004二分查询.md

@@ -46,7 +46,7 @@ def binary_search(a, x, start, end):
 a = [1, 2, 3, 5, 55, 66, 77, 88, 99, 100]
 x = 2
 
-binary_search(a, x, 0, len(a)
+binary_search(a, x, 0, len(a))
 # Print 1
 ```
 

013Trie树.md

@@ -117,4 +117,4 @@ print(tree.search("abcd"))
 # Print False
 ```
 
-这是本章内容，希望对你有所帮助。[进入下一章](./013Trie树.md)
+这是本章内容，希望对你有所帮助。[进入下一章](./014LRU缓存.md)

014LRU缓存.md

@@ -0,0 +1,70 @@
+
+# 实现LRUN缓存
+
+## 什么是LRU缓存
+
+LRU全称是Least Recently Used，也就是淘汰最晚使用的缓存技术，根据局部性原理，认为很久以前不用的数据最近也不会被使用。
+
+我们可以用不同的数据结构如数组、链表来实现LRU缓存，
+
+## 如何实现LRU缓存
+
+要实现LRU，其实只需要实现set()和get()两个方法即可，并且保证数组容量超过时按照LRU的策略进行移除对象，这里有个trick就是get或update对象时先移除对象再加入到队列中。
+
+Python的collections库中包含OrderedDict，可以更容易得实现LRU缓存，但为了避免高级特性我们还是使用array和dictionary来实现。
+
+```
+class LRUCache(object):
+
+    def __init__(self, capacity):
+        """
+        :type capacity: int
+        """
+        
+        self.capacity = capacity
+        # Example: ["k1", "k2"]
+        self.keys = []
+        # Example: {"k1": "v1"}, {"k2": "v2"}
+        self.data = {}
+        
+
+    def get(self, key):
+        """
+        :rtype: int
+        """
+        
+        # If match, update the index and return the data
+        if key in self.keys:
+            self.keys.remove(key)
+            self.keys.insert(0, key)
+            return self.data[key]
+        
+        # If no match, just return -1
+        else:
+            return -1
+        
+
+    def set(self, key, value):
+        """
+        :type key: int
+        :type value: int
+        :rtype: nothing
+        """
+        
+        # If there is the key
+        if key in self.keys:
+            self.data[key] = value
+            self.keys.remove(key)
+            self.keys.insert(0, key)
+            
+        # If there is no key and there's no capacity
+        elif len(self.keys) >= self.capacity:
+            self.keys.pop()
+            self.data[key] = value
+            self.keys.insert(0, key)
+            
+        # If there is no key and there is some capacity
+        else:
+            self.data[key] = value
+            self.keys.insert(0, key)
+```

lru.md

@@ -0,0 +1,57 @@
+
+```
+class LRUCache(object):
+
+    def __init__(self, capacity):
+        """
+        :type capacity: int
+        """
+        
+        self.capacity = capacity
+        # Example: [{"k1": "v1"}, {"k2": "v2"}]
+        self.items = []
+        
+
+    def get(self, key):
+        """
+        :rtype: int
+        """
+        
+        for i, kv in enumerate(self.items):
+            if kv.keys()[0] == key:
+                del(self.items[i])
+                self.items.insert(0, kv)
+                return kv.values()[0]
+                
+        # Return -1 if no match
+        return -1
+        
+
+    def set(self, key, value):
+        """
+        :type key: int
+        :type value: int
+        :rtype: nothing
+        """
+        
+        if len(self.items) == 0:
+            self.items.insert(0, {key: value})
+        
+        for i, kv in enumerate(self.items):
+            # If there is the key, just remove and insert in the head
+            if kv.keys()[0] == key:
+                del(self.items[i])
+                self.items.insert(0, {key: value})
+            # If there is no key and there's no capacity
+            elif len(self.items) >= self.capacity:
+                # Remove one
+                self.items.pop()
+            
+                # Insert one
+                self.items.insert(0, {key: value})
+            # If there is no key and there is some capacity
+            else:
+                # Insert one
+                self.items.insert(0, {key: value})
+```
+