From b6e9a40652d489605772f284ad2dac4a033fd216 Mon Sep 17 00:00:00 2001
From: TL <tommylohz@gmail.com>
Date: Tue, 26 Mar 2019 15:34:12 +0800
Subject: [PATCH] Update Shuffle

---
 Shuffle/README.markdown | 4 ++++
 Shuffle/Shuffle.swift   | 1 +
 2 files changed, 5 insertions(+)

diff --git a/Shuffle/README.markdown b/Shuffle/README.markdown
index d8ab7ff78..5a2a07a98 100644
--- a/Shuffle/README.markdown
+++ b/Shuffle/README.markdown
@@ -96,6 +96,8 @@ public func shuffledArray(_ n: Int) -> [Int] {
   var a = [Int](repeating: 0, count: n)
   for i in 0..<n {
     let j = Int.random(in: 0...i)
+    // for the Fisher–Yates_shuffle's pseudo code implement in wiki, it will check if i != j
+    a[i] = a[j]
     a[j] = i
   }
   return a
@@ -112,6 +114,8 @@ This returns something like `[3, 0, 9, 1, 8, 5, 2, 6, 7, 4]`. As you can see, ev
 
 The `shuffledArray()` function first creates a new array with `n` zeros. Then it loops `n` times and in each step adds the next number from the sequence to a random position in the array. The trick is to make sure that none of these numbers gets overwritten with the next one, so it moves the previous number out of the way first!
 
+For this function, `The condition that checks if j ≠ i may be omitted in languages that have no problems accessing uninitialized array values, and for which assigning is cheaper than comparing.`, you can check it in wiki. And also remove checking logic will optimise performance.
+
 The algoritm is quite clever and I suggest you walk through an example yourself, either on paper or in the playground. (Hint: Again it splits the array into two regions.)
 
 ## See also
diff --git a/Shuffle/Shuffle.swift b/Shuffle/Shuffle.swift
index a921e5ec3..1d2758c11 100644
--- a/Shuffle/Shuffle.swift
+++ b/Shuffle/Shuffle.swift
@@ -30,6 +30,7 @@ public func shuffledArray(_ n: Int) -> [Int] {
   var a = Array(repeating: 0, count: n)
   for i in 0..<n {
     let j = random(i + 1)
+    a[i] = a[j]
     a[j] = i  // insert next number from the sequence
   }
   return a