Implement in-place shuffle for arrays

Minor: reorder shuffle/shuffled extensions more consistently

#KT-25651 Fixed

libraries/stdlib/src/kotlin/collections/Collections.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2010-2018 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
  * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
  */
 
@@ -10,6 +10,7 @@
 package kotlin.collections
 
 import kotlin.contracts.*
+import kotlin.random.Random
 
 internal object EmptyIterator : ListIterator<Nothing> {
     override fun hasNext(): Boolean = false
@@ -266,6 +267,15 @@ public inline fun <C, R> C.ifEmpty(defaultValue: () -> R): R where C : Collectio
 @kotlin.internal.InlineOnly
 public inline fun <@kotlin.internal.OnlyInputTypes T> Collection<T>.containsAll(elements: Collection<T>): Boolean = this.containsAll(elements)
 
+
+/**
+ * Returns a new list with the elements of this list randomly shuffled
+ * using the specified [random] instance as the source of randomness.
+ */
+@SinceKotlin("1.3")
+public fun <T> Iterable<T>.shuffled(random: Random): List<T> = toMutableList().apply { shuffle(random) }
+
+
 internal fun <T> List<T>.optimizeReadOnlyList() = when (size) {
     0 -> emptyList()
     1 -> listOf(this[0])

libraries/stdlib/src/kotlin/collections/MutableCollections.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2010-2018 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
  * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
  */
 
@@ -225,14 +225,6 @@ private fun <T> MutableIterable<T>.filterInPlace(predicate: (T) -> Boolean, pred
 }
 
 
-/**
- * Returns a new list with the elements of this list randomly shuffled
- * using the specified [random] instance as the source of randomness.
- */
-@SinceKotlin("1.3")
-public fun <T> Iterable<T>.shuffled(random: Random): List<T> = toMutableList().apply { shuffle(random) }
-
-
 /**
  * Removes the element at the specified [index] from this list.
  * In Kotlin one should use the [MutableList.removeAt] function instead.
@@ -307,19 +299,3 @@ private fun <T> MutableList<T>.filterInPlace(predicate: (T) -> Boolean, predicat
         return false
     }
 }
-
-/**
- * Randomly shuffles elements in this mutable list using the specified [random] instance as the source of randomness.
- *
- * See: https://en.wikipedia.org/wiki/Fisher%E2%80%93Yates_shuffle#The_modern_algorithm
- */
-@SinceKotlin("1.3")
-public fun <T> MutableList<T>.shuffle(random: Random): Unit {
-    for (i in lastIndex downTo 1) {
-        val j = random.nextInt(i + 1)
-        val copy = this[i]
-        this[i] = this[j]
-        this[j] = copy
-    }
-}
-