Swift Implementation for LCCI 17.04

Author: klever34

lcci/17.04.Missing Number/README.md

@@ -119,6 +119,17 @@ var missingNumber = function (nums) {
 };
 ```
 
+```swift
+class Solution {
+    func missingNumber(_ nums: [Int]) -> Int {
+        let n = nums.count
+        let expectedSum = n * (n + 1) / 2
+        let actualSum = nums.reduce(0, +)
+        return expectedSum - actualSum
+    }
+}
+```
+
 <!-- tabs:end -->
 
 ### 方法二：求和

lcci/17.04.Missing Number/README_EN.md

@@ -119,6 +119,17 @@ var missingNumber = function (nums) {
 };
 ```
 
+```swift
+class Solution {
+    func missingNumber(_ nums: [Int]) -> Int {
+        let n = nums.count
+        let expectedSum = n * (n + 1) / 2
+        let actualSum = nums.reduce(0, +)
+        return expectedSum - actualSum
+    }
+}
+```
+
 <!-- tabs:end -->
 
 ### Solution 2

lcci/17.04.Missing Number/Solution.swift

@@ -0,0 +1,8 @@
+class Solution {
+    func missingNumber(_ nums: [Int]) -> Int {
+        let n = nums.count
+        let expectedSum = n * (n + 1) / 2
+        let actualSum = nums.reduce(0, +)
+        return expectedSum - actualSum
+    }
+}