From 465be0c0a4b009791f81a4f3b14634e8228a1c39 Mon Sep 17 00:00:00 2001
From: diegopetrucci <diegopetrucci@me.com>
Date: Sat, 12 Dec 2015 17:07:58 +0100
Subject: [PATCH 1/2] Solution for assignment #3 - Insertion Sort
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This code doesn’t actually work and I can’t understand why. Anyone can
help?
---
 .../Contents.swift                            | 68 +++++++++++++++----
 1 file changed, 55 insertions(+), 13 deletions(-)

diff --git a/Assignments/Sorting/ShellSort.playground/Pages/Shell Sort.xcplaygroundpage/Contents.swift b/Assignments/Sorting/ShellSort.playground/Pages/Shell Sort.xcplaygroundpage/Contents.swift
index 5161e34..683abf1 100644
--- a/Assignments/Sorting/ShellSort.playground/Pages/Shell Sort.xcplaygroundpage/Contents.swift	
+++ b/Assignments/Sorting/ShellSort.playground/Pages/Shell Sort.xcplaygroundpage/Contents.swift	
@@ -16,22 +16,22 @@ class ShellSequence: SequenceType {
     }
     
     func generate() -> AnyGenerator<Int> {
-        // YOUR CODE
+        var number = self.n
         
         return anyGenerator {
-            // YOUR CODE
-            
-            nil
+            number = number / 2
+            return number > 0 ? number : 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)) == [])
 
 
 /*:
@@ -41,6 +41,13 @@ class ShellSequence: SequenceType {
 Write a similar class to create a gap sequence of (3 ^ k  - 1) / 2) going as 1, 4, 13, 40, ... We will use the elements less than n in reversed order. For example if n is 200, the sequence should be [121, 40, 13, 4, 1].
 
 */
+// Defining ^ operator
+infix operator ** { associativity left precedence 170 }
+func ** (num: Int, power: Int) -> Int {
+    let numDouble = Double(num)
+    let powerDouble = Double(power)
+    return Int(pow(numDouble, powerDouble))
+}
 
 class KnuthSequence: SequenceType {
     let n: Int
@@ -51,14 +58,29 @@ class KnuthSequence: SequenceType {
     
     func generate() -> AnyGenerator<Int> {
         
+        var index = 1
+        
+        while (3 ** index - 1) / 2 < self.n {
+            index += 1
+        }
+        
+        index -= 1
+        
+        var number = (3 ** index - 1) / 2
+        
         return anyGenerator {
-            nil
+            print("index: \(index)")
+            print("number: \(number)")
+            number = (3 ** index - 1) / 2
+            index -= 1
+            return number > 1 ? number : nil
         }
     }
 }
 
-//assert(Array(KnuthSequence(n: 200)) == [121, 40, 13, 4, 1])
-//assert(Array(KnuthSequence(n: 10)) == [4, 1])
+// This assert (and the next ones) fails and I don't know why
+assert(Array(KnuthSequence(n: 200)) == [121, 40, 13, 4, 1])
+assert(Array(KnuthSequence(n: 10)) == [4, 1])
 
 /*:
 
@@ -70,8 +92,28 @@ 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] {
     
-    for i in KnuthSequence(n: array.count) {
+    
+
+    for gap in KnuthSequence(n: array.count) {
         
+        print("new smaller gap: \(gap)")
+        
+        var index = 0
+        var otherIndex = index + gap
+        
+        while otherIndex < array.count {
+            print("checking \(array[index]) and \(array[otherIndex])")
+            if isOrderedBefore(array[index], array[otherIndex]) == false {
+                swap(&array[index], &array[otherIndex])
+                print("swapped \(array[index]) with \(array[otherIndex])")
+                index = 0
+                otherIndex = index + gap
+            } else {
+                index += 1
+                otherIndex += 1
+                print("index + 1")
+            }
+        }
     }
     
     return array
@@ -79,7 +121,7 @@ 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
 
 assert(shellSort([Int](), isOrderedBefore: <).isSorted())

From 33ce6edfe037a9bc24d31211a2281bb68de00554 Mon Sep 17 00:00:00 2001
From: diegopetrucci <diegopetrucci@me.com>
Date: Tue, 15 Dec 2015 22:10:00 +0100
Subject: [PATCH 2/2] Fix Knuth Sequence

Thanks @matteomatassoni
---
 .../Pages/Shell Sort.xcplaygroundpage/Contents.swift            | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Assignments/Sorting/ShellSort.playground/Pages/Shell Sort.xcplaygroundpage/Contents.swift b/Assignments/Sorting/ShellSort.playground/Pages/Shell Sort.xcplaygroundpage/Contents.swift
index 683abf1..9ad8b33 100644
--- a/Assignments/Sorting/ShellSort.playground/Pages/Shell Sort.xcplaygroundpage/Contents.swift	
+++ b/Assignments/Sorting/ShellSort.playground/Pages/Shell Sort.xcplaygroundpage/Contents.swift	
@@ -73,7 +73,7 @@ class KnuthSequence: SequenceType {
             print("number: \(number)")
             number = (3 ** index - 1) / 2
             index -= 1
-            return number > 1 ? number : nil
+            return number > 0 ? number : nil
         }
     }
 }