From 83d671ffef065b3e841f44f3d693d5ab0cbe2e19 Mon Sep 17 00:00:00 2001
From: Mohit Cheppudira <mohit@muthanna.com>
Date: Sat, 7 Feb 2015 15:42:25 -0500
Subject: [PATCH] Fixed shuffle algorithm.

---
 go/shuffle/shuffle_test.go | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/go/shuffle/shuffle_test.go b/go/shuffle/shuffle_test.go
index 28a5846..13b58f5 100644
--- a/go/shuffle/shuffle_test.go
+++ b/go/shuffle/shuffle_test.go
@@ -9,7 +9,6 @@ package shuffle
 //    $ go test -benchmem -bench=. shuffle_test.go -benchtime=10s
 
 import (
-	"fmt"
 	"math/rand"
 	"reflect"
 	"testing"
@@ -30,8 +29,9 @@ func init() {
 
 // Native shuffle. No generics. Shuffle a slice of ints.
 func shuffle0(a []int) {
+	l := len(a)
 	for i := range a {
-		j := rand.Intn(i + 1)
+		j := i + rand.Intn(l-i)
 		a[i], a[j] = a[j], a[i]
 	}
 }
@@ -39,8 +39,9 @@ func shuffle0(a []int) {
 // Technique 1: requires user to convert specificially typed slice to
 // a slice of interface{}. Shuffles the copy in-place.
 func shuffle1(a []interface{}) {
+	l := len(a)
 	for i := range a {
-		j := rand.Intn(i + 1)
+		j := i + rand.Intn(l-i)
 		a[i], a[j] = a[j], a[i]
 	}
 }
@@ -62,9 +63,10 @@ func shuffle2(a interface{}) interface{} {
 func shuffle3(a interface{}) {
 	val := reflect.ValueOf(a)
 	tmp := reflect.New(val.Index(0).Type())
+	l := val.Len()
 
-	for i := 0; i < val.Len(); i++ {
-		j := rand.Intn(i + 1)
+	for i := 0; i < l; i++ {
+		j := i + rand.Intn(l-i)
 		tmp.Elem().Set(val.Index(j))
 		val.Index(j).Set(val.Index(i))
 		val.Index(i).Set(tmp.Elem())