adds pancake sort algorithm

azolinmf · azolinmf · commit 3affd0bc667d · 2021-10-13T11:12:26.000-03:00
diff --git a/DIRECTORY.md b/DIRECTORY.md
@@ -61,6 +61,7 @@
   * [Cocktailsort](https://github.com/TheAlgorithms/Swift/blob/master/sorts/CocktailSort.swift)
   * [Insertionsort](https://github.com/TheAlgorithms/Swift/blob/master/sorts/InsertionSort.swift)
   * [Mergesort](https://github.com/TheAlgorithms/Swift/blob/master/sorts/MergeSort.swift)
+  * [Pancakesort](https://github.com/TheAlgorithms/Swift/blob/master/sorts/PancakeSort.swift)
   * [Quicksort](https://github.com/TheAlgorithms/Swift/blob/master/sorts/QuickSort.swift)
   * [Selectionsort](https://github.com/TheAlgorithms/Swift/blob/master/sorts/SelectionSort.swift)
 
diff --git a/sorts/PancakeSort.swift b/sorts/PancakeSort.swift
@@ -0,0 +1,51 @@
+
+/*
+ Pancake sorting is the mathematical problem of sorting a disordered stack
+ of pancakes in order of size when a spatula can be inserted at any
+ point in the stack and used to flip all pancakes above it.
+ */
+
+import Foundation
+
+func flip(array: [Int], key: Int) -> [Int] {
+    var flippedArray = array
+    var pos = key
+    var start = 0
+    var aux = 0
+
+    while (start < pos) {
+        aux = flippedArray[start]
+        flippedArray[start] = flippedArray[pos]
+        flippedArray[pos] = aux
+        
+        start += 1
+        pos -= 1
+    }
+    
+    return flippedArray
+}
+
+func pancakeSort(_ array: [Int]) -> [Int] {
+    var list = array
+    var currentSize = list.count
+    for _ in (1 ..< currentSize).reversed() {
+        
+        let listToSearch = list[0...currentSize-1]
+        let max = listToSearch.max() ?? 0
+        let indexOfMax = listToSearch.firstIndex(of: max) ?? 0
+
+        if indexOfMax != currentSize - 1 {
+            list = flip(array: list, key: indexOfMax)
+            list = flip(array: list, key: currentSize - 1)
+        }
+        
+        currentSize -= 1
+    }
+    
+    return list
+}
+
+// The code below can be used for testing
+//var numbers = [2, 4, 6, 12, 3, -2, 9, 14, 22, 0, 18]
+//numbers = pancakeSort(numbers)
+//print(numbers)
