Assignment 3 solution

Assignments/Sorting/ShellSort.playground/Pages/Shell Sort.xcplaygroundpage/Contents.swift

@@ -16,22 +16,21 @@ class ShellSequence: SequenceType {
     }
 
     func generate() -> AnyGenerator<Int> {
-        // YOUR CODE
+        var m = n
 
         return anyGenerator {
-            // YOUR CODE
-
-            nil
+            m = m/2
+            return m >= 1 ? m : nil
         }
     }
 }
 
 //: Test your code with assert. Make sure asserts don't raise any errors.
 
-//assert(Array(ShellSequence(n: 20)) == [10, 5, 2, 1])
-//assert(Array(ShellSequence(n: 9)) == [4, 2, 1])
-//assert(Array(ShellSequence(n: 2)) == [1])
-//assert(Array(ShellSequence(n: 1)) == [])
+assert(Array(ShellSequence(n: 20)) == [10, 5, 2, 1])
+assert(Array(ShellSequence(n: 9)) == [4, 2, 1])
+assert(Array(ShellSequence(n: 2)) == [1])
+assert(Array(ShellSequence(n: 1)) == [])
 
 
 /*:
@@ -50,15 +49,25 @@ class KnuthSequence: SequenceType {
     }
 
     func generate() -> AnyGenerator<Int> {
+        var gaps = [Int]()
+        for i in 1...n/3 {
+            let x = (Int(pow(3.0, Double(i))) - 1) / 2
+            guard x < n else { break }
+            gaps.append(x)
+        }
+
+        gaps.sortInPlace(>)
+        var g = gaps.generate()
 
         return anyGenerator {
-            nil
+            return g.next()
         }
     }
 }
 
-//assert(Array(KnuthSequence(n: 200)) == [121, 40, 13, 4, 1])
-//assert(Array(KnuthSequence(n: 10)) == [4, 1])
+assert(Array(KnuthSequence(n: 200)) == [121, 40, 13, 4, 1])
+assert(Array(KnuthSequence(n: 10)) == [4, 1])
+assert(Array(KnuthSequence(n: 4)) == [1])
 
 /*:
 
@@ -69,8 +78,33 @@ Write a shell sort by using one of the generators you created above. Knuth's gap
 */
 
 func shellSort<T>(var array: [T], isOrderedBefore: (T, T) -> Bool) -> [T] {
+    guard array.count > 1 else { return array }
 
-    for i in KnuthSequence(n: array.count) {
+    for gap in KnuthSequence(n: array.count) {
+        print("gap \(gap)")
+
+        // Create a sub array of this gap's items
+        var subArray = [T]()
+        for i in 0.stride(to: array.count, by: gap) {
+            subArray.append(array[i])
+        }
+
+        // Sort that sub array using insertion sort
+        for i in 1..<subArray.count {
+            let currentItem = subArray[i]
+            var j = i
+            while j > 0 && isOrderedBefore(currentItem, subArray[j-1]) {
+                subArray[j] = subArray[j-1]
+                j--
+            }
+            subArray[j] = currentItem
+        }
+
+        // Update the original array with the sorted subArray's values
+        var g = subArray.generate()
+        for i in 0.stride(to: array.count, by: gap) {
+            array[i] = g.next()!
+        }
 
     }
 
@@ -79,14 +113,20 @@ func shellSort<T>(var array: [T], isOrderedBefore: (T, T) -> Bool) -> [T] {
 
 let items = ["c", "d", "b", "a"]
 let sortedItems = shellSort(items, isOrderedBefore: <)
-//assert(sortedItems.isSorted())
+assert(sortedItems.isSorted())
 assert(items == ["c", "d", "b", "a"]) // double check that items does not change
+let charArray = Array("A whole lot of text to sort so we get more than a few gaps. Also: Lorem Ipsum, or something.".characters)
+charArray.count
+let sortedCharArray = shellSort(charArray, isOrderedBefore: <)
+assert(sortedCharArray.isSorted())
+assert(sortedCharArray.count == charArray.count)
 
 assert(shellSort([Int](), isOrderedBefore: <).isSorted())
 assert(shellSort([1], isOrderedBefore: <).isSorted())
 assert(shellSort([1, 2, 3], isOrderedBefore: <).isSorted())
-//assert(shellSort([1, 2, 3], isOrderedBefore: >).isSorted(>))
-//assert(shellSort([3, 0, 2, 1, 2, -1], isOrderedBefore: <).isSorted())
+assert(shellSort([1, 2, 3], isOrderedBefore: >).isSorted(>))
+assert(shellSort([3, 0, 2, 1, 2, -1], isOrderedBefore: <).isSorted())
+assert(shellSort([3, 10, 23, 25, 1235, 234, 980, -3245, 0, 10, 89, 2, 200, 1, 100298, 2, 253, -983, 1039, -1], isOrderedBefore: <).isSorted())