To fix the sorted{ xxx } to sorted() & Add soapyigu flat-reduce solution

Signed-off-by: Desgard_Duan <[email protected]>

README.md

@@ -27,7 +27,7 @@
 * [Microsoft](#microsoft)
 
 ## Progress
-[Problem Status](#problem-status) shows the latest progress to all 500+ questions. Currently we have 219 completed solutions. Note: questions with ♥ mark means that you have to **Subscript to premium membership** of LeetCode to unlock them. Thank you for great contributions from [CharleneJiang](https://github.com/CharleneJiang), [ReadmeCritic](https://github.com/ReadmeCritic), [demonkoo](https://github.com/demonkoo), [DaiYue](https://github.com/DaiYue), [Quaggie](https://github.com/Quaggie) and [jindulys](https://github.com/jindulys).
+[Problem Status](#problem-status) shows the latest progress to all 500+ questions. Currently we have 221 completed solutions. Note: questions with ♥ mark means that you have to **Subscript to premium membership** of LeetCode to unlock them. Thank you for great contributions from [CharleneJiang](https://github.com/CharleneJiang), [ReadmeCritic](https://github.com/ReadmeCritic), [demonkoo](https://github.com/demonkoo), [DaiYue](https://github.com/DaiYue), [Quaggie](https://github.com/Quaggie) and [jindulys](https://github.com/jindulys).
 
 
 ## Array
@@ -189,7 +189,6 @@
 [Burst Ballons](https://leetcode.com/problems/burst-balloons/)| [Swift](./DP/BurstBalloons.swift)| Hard| O(n^3)| O(n)|
 [Frog Jump](https://leetcode.com/problems/frog-jump/)| [Swift](./DP/FrogJump.swift)| Hard| O(n^2)| O(n)|
 
-
 ## Depth-first search
 | Title | Solution | Difficulty | Time | Space |
 | ----- | -------- | ---------- | ---- | ----- |
@@ -771,4 +770,3 @@
 |	[Swift](./Math/AddTwoNumbers.swift)	|	2	|	[Add Two Numbers](https://leetcode.com/problems/add-two-numbers/)	| Medium	|
 |	[Swift](./Array/TwoSum.swift)	|	1	|	[Two Sum](https://leetcode.com/problems/two-sum/)	| Easy	|
 
-

Sort/ArrayPartitionI.swift

@@ -1,7 +1,7 @@
 class ArrayPartitionI {
     func arrayPairSum(_ nums: [Int]) -> Int {
         var arr = nums
-        arr = arr.sorted { $0 < $1 }
+        arr = arr.sorted()
         var res = 0
         for i in 0 ..< arr.count {
             if i & 1 != 0 {
@@ -11,3 +11,11 @@ class ArrayPartitionI {
         return res
     }
 }
+
+class ArrayPartitionI_2 {
+    func arrayPairSum(_ nums: [Int]) -> Int {
+        return nums.sorted(by: <).enumerated()
+            .flatMap { $0 % 2 == 0 ? $1 : nil }
+            .reduce(0) { $0 + $1 }
+    }
+}