update to match source

Author: TheIronBorn

Select Minimum Maximum/SelectMinimumMaximum.playground/Contents.swift

@@ -1,49 +1,44 @@
 // Compare each item to find minimum
 func minimum<T: Comparable>(_ array: [T]) -> T? {
-  var array = array
   guard !array.isEmpty else {
     return nil
   }
-  
-  var minimum = array.removeFirst()
-  for element in array {
+
+  var minimum = array.first!
+  for element in array.dropFirst() {
     minimum = element < minimum ? element : minimum
   }
   return minimum
 }
 
 // Compare each item to find maximum
 func maximum<T: Comparable>(_ array: [T]) -> T? {
-  var array = array
   guard !array.isEmpty else {
     return nil
   }
-  
-  var maximum = array.removeFirst()
-  for element in array {
+
+  var maximum = array.first!
+  for element in array.dropFirst() {
     maximum = element > maximum ? element : maximum
   }
   return maximum
 }
 
 // Compare in pairs to find minimum and maximum
 func minimumMaximum<T: Comparable>(_ array: [T]) -> (minimum: T, maximum: T)? {
-  var array = array
   guard !array.isEmpty else {
     return nil
   }
-  
+
   var minimum = array.first!
   var maximum = array.first!
-  
+
+  // if 'array' has an odd number of items, let 'minimum' or 'maximum' deal with the leftover
   let hasOddNumberOfItems = array.count % 2 != 0
-  if hasOddNumberOfItems {
-    array.removeFirst()
-  }
-  
-  while !array.isEmpty {
-    let pair = (array.removeFirst(), array.removeFirst())
-    
+  let start = hasOddNumberOfItems ? 1 : 0
+  for i in stride(from: start, to: array.count, by: 2) {
+    let pair = (array[i], array[i+1])
+
     if pair.0 > pair.1 {
       if pair.0 > maximum {
         maximum = pair.0
@@ -60,7 +55,7 @@ func minimumMaximum<T: Comparable>(_ array: [T]) -> (minimum: T, maximum: T)? {
       }
     }
   }
-  
+
   return (minimum, maximum)
 }