[DP] Add a solution to Wiggle Subsequence

Author: soapyigu

DP/WiggleSubsequence.swift

@@ -0,0 +1,25 @@
+/**
+ * Question Link: https://leetcode.com/problems/wiggle-subsequence/
+ * Primary idea: Classic Dynamic Programming, two variables/arries to track up or down status
+ * Time Complexity: O(n), Space Complexity: O(1)
+ */
+
+class WiggleSubsequence {
+    func wiggleMaxLength(_ nums: [Int]) -> Int {
+        guard nums.count >= 2 else {
+            return nums.count
+        }
+        
+        var up = 1, down = 1
+        
+        for i in 1..<nums.count {
+            if nums[i] > nums[i - 1] {
+                up = down + 1
+            } else if nums[i] < nums[i - 1] {
+                down = up + 1
+            } 
+        }
+        
+        return max(up, down)
+    }
+}

README.md

@@ -28,7 +28,7 @@
 * [Microsoft](#microsoft)
 
 ## Progress
-[Problem Status](#problem-status) shows the latest progress to all 800+ questions. Currently we have 242 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 243 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
@@ -200,6 +200,7 @@
 [Edit Distance](https://leetcode.com/problems/edit-distance/)| [Swift](./DP/EditDistance.swift)| Hard| O(mn)| O(mn)|
 [Combination Sum IV](https://leetcode.com/problems/combination-sum-iv/)| [Swift](./DP/CombinationSumIV.swift)| Medium| O(2^n)| O(n)|
 [Triangle](https://leetcode.com/problems/triangle/)| [Swift](./DP/Triangle.swift)| Medium| O(2^n)| O(m)|
+[Wiggle Subsequence](https://leetcode.com/problems/wiggle-subsequence/)| [Swift](./DP/WiggleSubsequence.swift)| Medium| O(n)| O(1)|
 [Wildcard Matching](https://leetcode.com/problems/wildcard-matching/)| [Swift](./DP/WildcardMatching.swift)| Hard| O(mn)| O(mn)|
 [Regular Expression Matching](https://leetcode.com/problems/regular-expression-matching/)| [Swift](./DP/RegularExpressionMatching.swift)| Hard| O(mn)| O(mn)|
 [Minimum Window Subsequence](https://leetcode.com/problems/minimum-window-subsequence/)| [Swift](./DP/MinimumWindowSubsequence.swift)| Hard| O(mn)| O(mn)|