Add solution to Strobogrammatic Number I and II

Array/StrobogrammaticNumber.swift

@@ -0,0 +1,38 @@
+/**
+ * Question Link: https://leetcode.com/problems/strobogrammatic-number/
+ * Primary idea: Two pointers, compare two characters until they are all valid
+ *
+ * Time Complexity: O(n), Space Complexity: O(1)
+ *
+ */
+
+ class StrobogrammaticNumber {
+    func isStrobogrammatic(_ num: String) -> Bool {
+        let numChars = Array(num)
+        var i = 0, j = num.count - 1
+
+        while i <= j {
+            if isValid(numChars[i], numChars[j]) {
+                i += 1
+                j -= 1
+            } else {
+                return false
+            }
+        }
+
+        return true
+    }
+
+    fileprivate func isValid(_ charA: Character, _ charB: Character) -> Bool {
+        if charA == charB {
+            return ["0", "1", "8"].contains(charA)
+        } else {
+            if (charA == "6" && charB == "9") || (charA == "9" && charB == "6") {
+                return true
+            } else {
+                return false
+            }
+        }
+    }
+}
+

DFS/StrobogrammaticNumberII.swift

@@ -0,0 +1,49 @@
+/**
+ * Question Link: https://leetcode.com/problems/strobogrammatic-number-ii/
+ * Primary idea: Classic DFS, set two places with correspond characters; 
+ *               starting from head and tail, and then move towards middle to cover all places.
+
+ * Time Complexity: O(m^n), here m is 5; Space Complexity: O(n)
+ *
+ */
+
+ class StrobogrammaticNumberII {
+    func findStrobogrammatic(_ n: Int) -> [String] {
+        var res = [String]()
+
+        guard n >= 1 else {
+            return res
+        }
+
+        let left = Array("01689"), right = Array("01986")
+        var path = Array(repeating: Character("-"), count: n)
+
+        dfs(&res, left, right, 0, n - 1, &path)
+
+        return res
+    }
+
+    fileprivate func dfs(_ res: inout [String], _ left: [Character], _ right: [Character], _ leftIdx: Int, _ path: inout [Character]) {
+    	let rightIdx = path.count - leftIdx - 1
+
+        if leftIdx > rightIdx {            
+            res.append(String(path))
+            return
+        }
+
+        for i in 0..<left.count {
+            if leftIdx == 0 && leftIdx != rightIdx && left[i] == "0" {
+                continue
+            }
+
+            if leftIdx == rightIdx && (left[i] == "6" || left[i] == "9") {
+                continue
+            }
+
+            path[leftIdx] = left[i]
+            path[rightIdx] = right[i]
+
+            dfs(&res, left, right, leftIdx + 1, rightIdx - 1, &path)
+        }
+    }
+}

README.md

@@ -28,7 +28,7 @@
 * [Microsoft](#microsoft)
 
 ## Progress
-[Problem Status](#problem-status) shows the latest progress to all 800+ questions. Currently we have 253 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 255 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
@@ -48,6 +48,7 @@
 [Remove Duplicates from Sorted Array II](https://leetcode.com/problems/remove-duplicates-from-sorted-array-ii/)| [Swift](./Array/RemoveDuplicatesFromSortedArrayII.swift)| Medium| O(n)| O(1)|
 [Move Zeroes](https://leetcode.com/problems/move-zeroes/)| [Swift](./Array/MoveZeroes.swift)| Easy| O(n)| O(1)|
 [Remove Element](https://leetcode.com/problems/remove-element/)| [Swift](./Array/RemoveElement.swift)| Easy| O(n)| O(1)|
+[Strobogrammatic Number](https://leetcode.com/problems/strobogrammatic-number/)| [Swift](./Array/StrobogrammaticNumber.swift)| Easy| O(n)| O(1)|
 [Two Sum](https://leetcode.com/problems/two-sum/)| [Swift](./Array/TwoSum.swift)| Easy| O(n)| O(n)|
 [3Sum](https://leetcode.com/problems/3sum/)| [Swift](./Array/ThreeSum.swift)| Medium| O(n^2)| O(nC3)|
 [3Sum Closest](https://leetcode.com/problems/3sum-closest/)| [Swift](./Array/ThreeSum.swift)| Medium| O(n^2)| O(nC3)|
@@ -226,6 +227,7 @@
 [Combination Sum III](https://leetcode.com/problems/combination-sum-iii/)| [Swift](./DFS/CombinationSumIII.swift)| Medium| O(n!)| O(nCk)|
 [Letter Combinations of a Phone Number](https://leetcode.com/problems/letter-combinations-of-a-phone-number/)| [Swift](./DFS/LetterCombinationsPhoneNumber.swift)| Medium| O(mn)| O(n)|
 [Factor Combinations](https://leetcode.com/problems/factor-combinations/)| [Swift](./DFS/FactorCombinations.swift)| Medium| O(n^n))| O(2^n - 1)|
+[Strobogrammatic Number II](https://leetcode.com/problems/strobogrammatic-number-ii/)| [Swift](./DFS/StrobogrammaticNumberII.swift)| Medium| O(m^n)| O(n)|
 [Generalized Abbreviation](https://leetcode.com/problems/generalized-abbreviation/)| [Swift](./DFS/GeneralizedAbbreviation.swift)| Medium| O(n!)| O(2^n)|
 [Palindrome Partitioning](https://leetcode.com/problems/palindrome-partitioning/)| [Swift](./DFS/PalindromePartitioning.swift)| Medium| O(n!)| O(n)|
 [Is Graph Bipartite](https://leetcode.com/problems/is-graph-bipartite/)| [Swift](./DFS/IsGraphBipartite.swift)| Medium| O(n)| O(n)|
@@ -580,8 +582,8 @@
 |		|	250	|	[Count Univalue Subtrees](https://leetcode.com/problems/count-univalue-subtrees/) ♥	|	Medium	|
 |		|	249	|	[Group Shifted Strings](https://leetcode.com/problems/group-shifted-strings/) ♥	| Easy	|
 |		|	248	|	[Strobogrammatic Number III](https://leetcode.com/problems/strobogrammatic-number-iii/) ♥	|	Hard	|
-|		|	247	|	[Strobogrammatic Number II](https://leetcode.com/problems/strobogrammatic-number-ii/) ♥	|	Medium	|
-|		|	246	|	[Strobogrammatic Number](https://leetcode.com/problems/strobogrammatic-number/) ♥	| Easy	|
+|	[Swift](./DFS/StrobogrammaticNumberII.swift)	|	247	|	[Strobogrammatic Number II](https://leetcode.com/problems/strobogrammatic-number-ii/) ♥	|	Medium	|
+|	[Swift](./Array/StrobogrammaticNumber.swift)	|	246	|	[Strobogrammatic Number](https://leetcode.com/problems/strobogrammatic-number/) ♥	| Easy	|
 |	[Swift](./Array/ShortestWordDistanceIII.swift)	|	245	|	[Shortest Word Distance III](https://leetcode.com/problems/shortest-word-distance-iii/) ♥	|	Medium	|
 |		|	244	|	[Shortest Word Distance II](https://leetcode.com/problems/shortest-word-distance-ii/) ♥	|	Medium	|
 | [Swift](./String/ShortestWordDistance.swift)	|	243	|	[Shortest Word Distance](https://leetcode.com/problems/shortest-word-distance/) ♥	| Easy	|