feat: add swift implementation to lcof2 problem: No.031

lcof2/剑指 Offer II 031. 最近最少使用缓存/README.md

@@ -667,6 +667,99 @@ public class LRUCache {
  */
 ```
 
+#### Swift
+
+```swift
+class Node {
+    var key: Int
+    var val: Int
+    var prev: Node?
+    var next: Node?
+
+    init() {
+        self.key = 0
+        self.val = 0
+    }
+
+    init(_ key: Int, _ val: Int) {
+        self.key = key
+        self.val = val
+    }
+}
+
+class LRUCache {
+    private var cache = [Int: Node]()
+    private let head: Node
+    private let tail: Node
+    private let capacity: Int
+    private var size: Int
+
+    init(_ capacity: Int) {
+        self.capacity = capacity
+        self.size = 0
+        self.head = Node()
+        self.tail = Node()
+        head.next = tail
+        tail.prev = head
+    }
+
+    func get(_ key: Int) -> Int {
+        guard let node = cache[key] else {
+            return -1
+        }
+        moveToHead(node)
+        return node.val
+    }
+
+    func put(_ key: Int, _ value: Int) {
+        if let node = cache[key] {
+            node.val = value
+            moveToHead(node)
+        } else {
+            let newNode = Node(key, value)
+            cache[key] = newNode
+            addToHead(newNode)
+            size += 1
+            if size > capacity {
+                let tail = removeTail()
+                cache.removeValue(forKey: tail.key)
+                size -= 1
+            }
+        }
+    }
+
+    private func moveToHead(_ node: Node) {
+        removeNode(node)
+        addToHead(node)
+    }
+
+    private func removeNode(_ node: Node) {
+        node.prev?.next = node.next
+        node.next?.prev = node.prev
+    }
+
+    private func addToHead(_ node: Node) {
+        node.next = head.next
+        node.prev = head
+        head.next?.prev = node
+        head.next = node
+    }
+
+    private func removeTail() -> Node {
+        let node = tail.prev!
+        removeNode(node)
+        return node
+    }
+}
+
+/**
+ * Your LRUCache object will be instantiated and called as such:
+ * let obj = LRUCache(capacity)
+ * let ret_1: Int = obj.get(key)
+ * obj.put(key, value)
+ */
+```
+
 <!-- tabs:end -->
 
 <!-- solution:end -->

lcof2/剑指 Offer II 031. 最近最少使用缓存/Solution.swift

@@ -0,0 +1,88 @@
+class Node {
+    var key: Int
+    var val: Int
+    var prev: Node?
+    var next: Node?
+
+    init() {
+        self.key = 0
+        self.val = 0
+    }
+
+    init(_ key: Int, _ val: Int) {
+        self.key = key
+        self.val = val
+    }
+}
+
+class LRUCache {
+    private var cache = [Int: Node]()
+    private let head: Node
+    private let tail: Node
+    private let capacity: Int
+    private var size: Int
+
+    init(_ capacity: Int) {
+        self.capacity = capacity
+        self.size = 0
+        self.head = Node()
+        self.tail = Node()
+        head.next = tail
+        tail.prev = head
+    }
+
+    func get(_ key: Int) -> Int {
+        guard let node = cache[key] else {
+            return -1
+        }
+        moveToHead(node)
+        return node.val
+    }
+
+    func put(_ key: Int, _ value: Int) {
+        if let node = cache[key] {
+            node.val = value
+            moveToHead(node)
+        } else {
+            let newNode = Node(key, value)
+            cache[key] = newNode
+            addToHead(newNode)
+            size += 1
+            if size > capacity {
+                let tail = removeTail()
+                cache.removeValue(forKey: tail.key)
+                size -= 1
+            }
+        }
+    }
+
+    private func moveToHead(_ node: Node) {
+        removeNode(node)
+        addToHead(node)
+    }
+
+    private func removeNode(_ node: Node) {
+        node.prev?.next = node.next
+        node.next?.prev = node.prev
+    }
+
+    private func addToHead(_ node: Node) {
+        node.next = head.next
+        node.prev = head
+        head.next?.prev = node
+        head.next = node
+    }
+
+    private func removeTail() -> Node {
+        let node = tail.prev!
+        removeNode(node)
+        return node
+    }
+}
+
+/**
+ * Your LRUCache object will be instantiated and called as such:
+ * let obj = LRUCache(capacity)
+ * let ret_1: Int = obj.get(key)
+ * obj.put(key, value)
+ */