[Design] Add a solution to All O`one Data Structure

Design/AllOne.swift

@@ -0,0 +1,152 @@
+/**
+ * Question Link: https://leetcode.com/problems/all-oone-data-structure/
+ * Primary idea: Use a doubly linked list while the node is val and all keys, and 
+ *				 a hash table where value is the node containing the key
+ * Time Complexity: O(1), Space Complexity: O(n)
+ *
+ */
+
+ class AllOne {
+
+    private var dict: [String: Node]
+
+    private var head: Node
+    private var tail: Node
+
+    /** Initialize your data structure here. */
+    init() {
+        dict = [String: Node]()
+
+        head = Node(-1, "")
+        tail = Node(-1, "")
+        head.post = tail
+        tail.prev = head
+    }
+
+    /** Inserts a new key <Key> with value 1. Or increments an existing key by 1. */
+    func inc(_ key: String) {
+        if let node = dict[key] {
+            update(node, key, 1)
+        } else {
+            if head.post!.val != 1 {
+                let node = Node(1, key)
+                insert(node, after: head)
+                dict[key] = node
+            } else {
+                head.post!.list.insert(key)
+                dict[key] = head.post!
+            }
+        }
+    }
+
+    /** Decrements an existing key by 1. If Key's value is 1, remove it from the data structure. */
+    func dec(_ key: String) {
+        guard let node = dict[key] else {
+            return
+        }
+
+        update(node, key, -1)
+    }
+
+    /** Returns one of the keys with maximal value. */
+    func getMaxKey() -> String {
+        if dict.count > 0 {
+            return tail.prev!.list.first!
+        } else {
+            return ""
+        }
+    }
+
+    /** Returns one of the keys with Minimal value. */
+    func getMinKey() -> String {
+        if dict.count > 0 {
+            return head.post!.list.first!
+        } else {
+            return ""
+        }
+    }
+
+    private func update(_ node: Node, _ key: String, _ addVal: Int) {
+        node.list.remove(key)
+
+        let next = addVal == 1 ? node.post : node.prev
+
+        // insert new node
+        if next!.val != node.val + addVal {
+            guard node.val + addVal != 0 else {
+                dict[key] = nil
+
+                removeIfNecessary(node)
+
+                return
+            }
+
+            let newNode = Node(node.val + addVal, key)
+
+            if addVal == 1 {
+                insert(newNode, after: node)
+            } else {
+                insert(newNode, before: node)
+            }
+
+            dict[key] = newNode
+
+        // insert key to next node
+        } else {
+            next!.list.insert(key)
+            dict[key] = next
+        }
+
+        removeIfNecessary(node)
+    }
+
+    private func insert(_ newNode: Node, after node: Node) {
+        node.post?.prev = newNode
+        newNode.post = node.post
+
+        newNode.prev = node
+        node.post = newNode 
+    }
+
+    private func insert(_ newNode: Node, before node: Node) {
+        node.prev?.post = newNode
+        newNode.prev = node.prev
+
+        newNode.post = node
+        node.prev = newNode  
+    }
+
+    private func removeIfNecessary(_ node: Node) {   
+        guard node.list.isEmpty else {
+            return
+        }
+
+        node.post!.prev = node.prev
+        node.prev!.post = node.post
+
+        node.prev = nil
+        node.post = nil
+
+    }
+}
+
+fileprivate class Node {
+    var val: Int
+    var list: Set<String>
+    var prev: Node?
+    var post: Node?
+
+    init(_ val: Int, _ key: String) {
+        self.val = val
+        list = Set<String>([key])
+    }
+}
+
+/**
+ * Your AllOne object will be instantiated and called as such:
+ * let obj = AllOne()
+ * obj.inc(key)
+ * obj.dec(key)
+ * let ret_3: String = obj.getMaxKey()
+ * let ret_4: String = obj.getMinKey()
+ */

README.md

@@ -4,7 +4,7 @@
 ![Leetcode](./logo.png?style=centerme)
 
 ## Progress
-[Problem Status](#problem-status) shows the latest progress to all 1000+ questions. Currently we have 311 completed solutions. Note: questions with ♥ mark means that you have to **Subscript to premium membership** of LeetCode to unlock them.
+[Problem Status](#problem-status) shows the latest progress to all 1000+ questions. Currently we have 312 completed solutions. Note: questions with ♥ mark means that you have to **Subscript to premium membership** of LeetCode to unlock them.
 
 ## Contributors
 
@@ -397,6 +397,7 @@
 [Add and Search Word - Data structure design](https://leetcode.com/problems/add-and-search-word-data-structure-design/)| [Swift](./Design/AddSearchWord.swift)| Medium | O(24^n)| O(n)|
 [Insert Delete GetRandom O(1)](https://leetcode.com/problems/insert-delete-getrandom-o1/)| [Swift](./Design/InsertDeleteGetRandom.swift)| Medium| O(1)| O(n)|
 [LRU Cache](https://leetcode.com/problems/lru-cache/)| [Swift](./Design/LRUCache.swift)| Hard| O(1)| O(n)|
+[All O`one Data Structure](https://leetcode.com/problems/all-oone-data-structure/)| [Swift](./Design/AllOne.swift)| Hard| O(1)| O(n)|
 
 
 ## Google