[String] Add a solution to Reverse Words in a String I, II, and III

Author: soapyigu

README.md

@@ -28,7 +28,7 @@
 * [Microsoft](#microsoft)
 
 ## Progress
-[Problem Status](#problem-status) shows the latest progress to all 800+ questions. Currently we have 266 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 269 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
@@ -96,6 +96,9 @@
 [Reverse String](https://leetcode.com/problems/reverse-string/)| [Swift](./String/ReverseString.swift)| Easy| O(n)| O(n)|
 [Reverse String II](https://leetcode.com/problems/reverse-string-ii/)| [Swift](./String/ReverseStringII.swift)| Easy| O(n)| O(n)|
 [Reverse Vowels of a String](https://leetcode.com/problems/reverse-vowels-of-a-string/)| [Swift](./String/ReverseVowelsOfAString.swift)| Easy| O(n)| O(n)|
+[Reverse Words in a String](https://leetcode.com/problems/reverse-words-in-a-string/)| [Swift](./String/ReverseWordsString.swift)| Medium| O(n)| O(1)|
+[Reverse Words in a String II](https://leetcode.com/problems/reverse-words-in-a-string-ii/)| [Swift](./String/ReverseWordsStringII.swift)| Medium| O(n)| O(1)|
+[Reverse Words in a String III](https://leetcode.com/problems/reverse-words-in-a-string-iii/)| [Swift](./String/ReverseWordsStringIII.swift)| Easy| O(n)| O(1)|
 [Length of Last Word](https://leetcode.com/problems/length-of-last-word/)| [Swift](./String/AddStrings.swift)| Easy| O(n)| O(n)|
 [String Compression](https://leetcode.com/problems/string-compression/)| [Swift](./String/StringCompression.swift)| Easy| O(n)| O(1)|
 [Add Strings](https://leetcode.com/problems/add-strings/)| [Swift](./String/LengthLastWord.swift)| Easy| O(n)| O(1)|
@@ -649,7 +652,7 @@
 |	[Swift](./Array/RotateArray.swift)	|	189	|	[Rotate Array](https://oj.leetcode.com/problems/rotate-array/)	| Easy	|
 |	[Swift](./DP/BestTimeBuySellStockIV.swift)	|	188	|	[Best Time to Buy and Sell Stock IV](https://oj.leetcode.com/problems/best-time-to-buy-and-sell-stock-iv/)	| Hard	|
 |		|	187	|	[Repeated DNA Sequences](https://oj.leetcode.com/problems/repeated-dna-sequences/)	| Medium	|
-|		|	186	|	[Reverse Words in a String II](https://oj.leetcode.com/problems/reverse-words-in-a-string-ii/) ♥	| Medium	|
+|	[Swift](./String/ReverseWordsStringII.swift)	|	186	|	[Reverse Words in a String II](https://oj.leetcode.com/problems/reverse-words-in-a-string-ii/) ♥	| Medium	|
 |		|	179	|	[Largest Number](https://oj.leetcode.com/problems/largest-number/)	| Medium	|
 |		|	174	|	[Dungeon Game](https://oj.leetcode.com/problems/dungeon-game/)	| Hard	|
 |		|	173	|	[Binary Search Tree Iterator](https://oj.leetcode.com/problems/binary-search-tree-iterator/)	| Medium	|
@@ -674,7 +677,7 @@
 |	[Swift](./Search/FindMinimumRotatedSortedArrayII.swift)	|	154	|	[Find Minimum in Rotated Sorted Array II](https://oj.leetcode.com/problems/find-minimum-in-rotated-sorted-array-ii/)	| Hard	|
 |	[Swift](./Search/FindMinimumRotatedSortedArray.swift)	|	153	|	[Find Minimum in Rotated Sorted Array](https://oj.leetcode.com/problems/find-minimum-in-rotated-sorted-array/)	| Medium	|
 |	[Swift](./DP/MaximumProductSubarray.swift)	|	152	|	[Maximum Product Subarray](https://oj.leetcode.com/problems/maximum-product-subarray/)	| Medium	|
-|		|	151	|	[Reverse Words in a String](https://oj.leetcode.com/problems/reverse-words-in-a-string/)	| Medium	|
+|	[Swift](./String/ReverseWordsString.swift)	|	151	|	[Reverse Words in a String](https://oj.leetcode.com/problems/reverse-words-in-a-string/)	| Medium	|
 |	[Swift](./Stack/EvaluateReversePolishNotation.swift)	|	150	|	[Evaluate Reverse Polish Notation](https://oj.leetcode.com/problems/evaluate-reverse-polish-notation/)	| Medium	|
 |		|	149	|	[Max Points on a Line](https://oj.leetcode.com/problems/max-points-on-a-line/)	| Hard	|
 |		|	148	|	[Sort List](https://oj.leetcode.com/problems/sort-list/)	| Medium	|

String/ReverseString.swift

@@ -8,6 +8,6 @@
 
 class ReverseString {
     func reverseString(s: String) -> String {
-        return String(s.characters.reverse())
+        return String(s.reversed())
     }
 }

String/ReverseWordsString.swift

@@ -0,0 +1,13 @@
+/**
+ * Question Link: https://leetcode.com/problems/reverse-words-in-a-string/
+ * Primary idea: Trim and split the original string, add word from end to start
+ * 
+ * Time Complexity: O(n), Space Complexity: O(1)
+ *
+ */
+
+class ReverseWordsString {
+	func reverseWords(_ s: String) -> String {
+	  	return String(s.split(separator: " ").reversed().reduce("") { total, word in total + word + " "}.dropLast())
+	}
+}

String/ReverseWordsStringII.swift

@@ -0,0 +1,32 @@
+/**
+ * Question Link: https://leetcode.com/problems/reverse-words-in-a-string-ii/
+ * Primary idea: Reverse the whole string, then reverse every word
+ * 
+ * Time Complexity: O(n), Space Complexity: O(1)
+ *
+ */
+
+ class ReverseWordsStringII {
+    func reverseWords(_ str: inout [Character]) {
+        var last = 0
+        
+        reverse(&str, 0, str.count - 1)
+        
+        for i in 0..<str.count {
+            if i + 1 == str.count || (str[i] != " " && str[i + 1] == " ") {
+                reverse(&str, last, i)
+                last = i + 2
+            }
+        }
+    }
+    
+    fileprivate func reverse<T>(_ array: inout [T], _ startIdx: Int, _ endIdx: Int) {
+        var (left, right) = (startIdx, endIdx)
+  
+        while left < right {
+            (array[left], array[right]) = (array[right], array[left])
+            left += 1
+            right -= 1
+        }
+    }
+}

String/ReverseWordsStringIII.swift

@@ -0,0 +1,32 @@
+/**
+ * Question Link: https://leetcode.com/problems/reverse-words-in-a-string-iii/
+ * Primary idea: Check the empty space to get the previous word, then reverse it
+ * 
+ * Time Complexity: O(n), Space Complexity: O(1)
+ *
+ */
+
+ class ReverseWordsStringIII {
+    func reverseWords(_ s: String) -> String {
+        var last = 0, str = Array(s)
+        
+        for i in 0..<str.count {
+            if i + 1 == str.count || (str[i] != " " && str[i + 1] == " ") {
+                reverse(&str, last, i)
+                last = i + 2
+            }
+        }
+        
+        return String(str)
+    }
+    
+    fileprivate func reverse<T>(_ array: inout [T], _ startIdx: Int, _ endIdx: Int) {
+        var (left, right) = (startIdx, endIdx)
+  
+        while left < right {
+            (array[left], array[right]) = (array[right], array[left])
+            left += 1
+            right -= 1
+        }
+    }
+}