Assignment002 solutions

Assignments/Sorting/InsertionSort.playground/Pages/Insertion Sort.xcplaygroundpage/Contents.swift

@@ -6,10 +6,30 @@ Write an `insertionSort` function that takes an array and returns it as sorted b
 Note that there is already a `swap` function in the standard library. However, you can move the larger elements to the right rather than using the `swap` function.
 
 */
+extension Array {
+  func insertInOrder(newElement: Element, @noescape isOrderedBefore: (Element, Element) -> Bool) -> [Element] {
+    var array = self
+    guard !array.isEmpty else {
+      return [newElement]
+    }
+
+    let firstElement = array.removeFirst()
+    if isOrderedBefore(newElement, firstElement) {
+      return [newElement, firstElement] + array
+    } else {
+      return [firstElement] + array.insertInOrder(newElement, isOrderedBefore: isOrderedBefore)
+    }
+  }
+}
 
 func insertionSort<T>(var array: [T], @noescape isOrderedBefore: (T, T) -> Bool) -> [T] {
-
-    return array
+  guard !array.isEmpty else {
+    return []
+  }
+
+  let firstElement = array.removeFirst() // this removes the first element from the array mutating it
+  let subOrderedArray = insertionSort(array, isOrderedBefore: isOrderedBefore) // recursive call on the smaller array
+  return subOrderedArray.insertInOrder(firstElement, isOrderedBefore: isOrderedBefore) // insert the first element mainting the order in the subarray, which is ordered
 }
 
 
@@ -22,8 +42,8 @@ assert(items == ["c", "d", "b"]) // double check that items does not change
 
 assert(insertionSort([1], isOrderedBefore: <).isSorted())
 assert(insertionSort([1, 2, 3], isOrderedBefore: <).isSorted())
-//assert(insertionSort([1, 2, 3], isOrderedBefore: >).isSorted(>))
-//assert(insertionSort([3, 2, 1, 2, -1], isOrderedBefore: <).isSorted())
+assert(insertionSort([1, 2, 3], isOrderedBefore: >).isSorted(>))
+assert(insertionSort([3, 2, 1, 2, -1], isOrderedBefore: <).isSorted())
 
 /*:
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