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

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

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 }
+    }
+}