[DP] Add a new solution to Flip Game II

DP/FlipGameII.swift

@@ -0,0 +1,39 @@
+/**
+ * Question Link: https://leetcode.com/problems/flip-game-ii/
+ * Primary idea: Classic DP, using a map to memorize previous step
+ * Time Complexity: O(n), Space Complexity: O(n)
+ */
+
+class FlipGameII {
+    func canWin(_ s: String) -> Bool {
+        var winMap = [String: Bool]()
+
+        return helper(s, &winMap)
+    }
+
+    func helper(_ s: String, _ winMap: inout [String: Bool]) -> Bool {
+        guard s.count >= 2 else {
+            return false
+        }
+
+        if let sWin = winMap[s] {
+            return sWin
+        }
+
+        let sChars = Array(s)
+
+        for i in 0..<sChars.count - 1 {
+            guard sChars[i] == sChars[i + 1] && sChars[i] == "+" else {
+                continue
+            }
+
+            if !helper(String(sChars[0..<i] + "--" + sChars[i + 2..<sChars.count]), &winMap) {
+                winMap[s] = true
+                return true
+            }
+        }
+
+        winMap[s] = false
+        return false
+    }
+}

README.md

@@ -28,7 +28,7 @@
 * [Microsoft](#microsoft)
 
 ## Progress
-[Problem Status](#problem-status) shows the latest progress to all 800+ questions. Currently we have 240 completed solutions. Note: questions with ♥ mark means that you have to **Subscript to premium membership** of LeetCode to unlock them. Thank you for great contributions from [CharleneJiang](https://github.com/CharleneJiang), [ReadmeCritic](https://github.com/ReadmeCritic), [demonkoo](https://github.com/demonkoo), [DaiYue](https://github.com/DaiYue), [Quaggie](https://github.com/Quaggie) and [jindulys](https://github.com/jindulys).
+[Problem Status](#problem-status) shows the latest progress to all 800+ questions. Currently we have 241 completed solutions. Note: questions with ♥ mark means that you have to **Subscript to premium membership** of LeetCode to unlock them. Thank you for great contributions from [CharleneJiang](https://github.com/CharleneJiang), [ReadmeCritic](https://github.com/ReadmeCritic), [demonkoo](https://github.com/demonkoo), [DaiYue](https://github.com/DaiYue), [Quaggie](https://github.com/Quaggie) and [jindulys](https://github.com/jindulys).
 
 
 ## Array
@@ -174,6 +174,7 @@
 [Min Cost Climbing Stairs](https://leetcode.com/problems/min-cost-climbing-stairs/)| [Swift](./DP/MinCostClimbingStairs.swift)| Easy| O(n)| O(n)|
 [Unique Paths](https://leetcode.com/problems/unique-paths/)| [Swift](./DP/UniquePaths.swift)| Medium| O(mn)| O(mn)|
 [Unique Paths II](https://leetcode.com/problems/unique-paths-ii/)| [Swift](./DP/UniquePathsII.swift)| Medium| O(mn)| O(mn)|
+[Flip Game II](https://leetcode.com/problems/flip-game-ii/)| [Swift](./DP/FlipGameII.swift)| Medium| O(n)| O(n)|
 [Decode Ways](https://leetcode.com/problems/decode-ways/)| [Swift](./DP/DecodeWays.swift) | O(n)|O(n)|
 [Minimum Path Sum](https://leetcode.com/problems/minimum-path-sum/)| [Swift](./DP/MinimumPathSum.swift)| Medium| O(mn)| O(mn)|
 [Generate Parentheses](https://leetcode.com/problems/generate-parentheses/)| [Swift](./DP/GenerateParentheses.swift)| Medium| O(2^n)| O(n)|
@@ -521,7 +522,7 @@
 |		|	297	|	[Serialize and Deserialize Binary Tree](https://leetcode.com/problems/serialize-and-deserialize-binary-tree/)	|	Hard	|
 |	[Swift](./Tree/UniqueBinarySearchTrees.swift)	|	296	|	[Best Meeting Point](https://leetcode.com/problems/best-meeting-point/) ♥	|	Hard	|
 |		|	295	|	[Find Median from Data Stream](https://leetcode.com/problems/find-median-from-data-stream/)	|	Hard	|
-|		|	294	|	[Flip Game II](https://leetcode.com/problems/flip-game-ii/) ♥	|	Medium	|
+|	[Swift](./DP/FlipGameII.swift)	|	294	|	[Flip Game II](https://leetcode.com/problems/flip-game-ii/) ♥	|	Medium	|
 |	[Swift](./String/FlipGame.swift)	|	293	|	[Flip Game](https://leetcode.com/problems/flip-game/) ♥	| Easy	|
 |		|	292	|	[Nim Game](https://leetcode.com/problems/nim-game/)	| Easy	|
 |		|	291	|	[Word Pattern II](https://leetcode.com/problems/word-pattern-ii/) ♥	|	Hard	|

String/FlipGame.swift

@@ -5,19 +5,17 @@
  */
 
 class FlipGame {
-    func generatePossibleNextMoves(s: String) -> [String] {
+    func generatePossibleNextMoves(_ s: String) -> [String] {
         var res = [String]()
-        var sChars = Array(s.characters)
+        let sChars = Array(s)
 
         guard sChars.count > 1 else {
             return res
         }
 
         for i in 0..<sChars.count - 1 {
             if sChars[i] == "+" && sChars[i + 1] == "+" {
-                var temp = sChars
-                (temp[i], temp[i + 1])  = ("-", "-")
-                res.append(String(temp))
+                res.append(String(sChars[0..<i] + "--" + sChars[i + 2..<sChars.count]))
             }
         }