add deck shuffle with proper randomising

Author: andriesniemandt

.gitignore

@@ -1 +1 @@
-.idea
+.idea/

README.md

@@ -1,22 +1,25 @@
 package main
 
-import "fmt"
+import (
+	"fmt"
+	"math/rand"
+	"time"
+)
 
 // Create a new type of 'deck'
 // type deck is a slice of strings
-type deck [] string
+type deck []string
 
 func newDeck() deck {
-	cards := deck {}
-
-	cardSuits := [] string {
+	cards := deck{}
+	cardSuits := []string{
 		"Spades",
 		"Diamonds",
 		"Hearts",
 		"Clubs",
 	}
 
-	cardValues := [] string {
+	cardValues := []string{
 		"Ace",
 		"Two",
 		"Three",
@@ -34,10 +37,9 @@ func newDeck() deck {
 
 	for _, suit := range cardSuits {
 		for _, value := range cardValues {
-			cards = append(cards, value + " of " + suit)
+			cards = append(cards, value+" of "+suit)
 		}
 	}
-
 	return cards
 }
 
@@ -46,3 +48,15 @@ func (d deck) print() {
 		fmt.Println(i, card)
 	}
 }
+
+func (d deck) shuffle() {
+	source := rand.NewSource(time.Now().UnixNano())
+	r := rand.New(source)
+
+	for i := range d {
+		newPosition := r.Intn(len(d) - 1)
+		// One line index swap
+		// x,y = y,x
+		d[i], d[newPosition] = d[newPosition], d[i]
+	}
+}

deck.go

@@ -2,5 +2,6 @@ package main
 
 func main() {
 	cards := newDeck()
+	cards.shuffle()
 	cards.print()
-}
+}