feat: add swift implementation to lcof problem: No.50 (#2935)

Author: klever34

lcof/面试题50. 第一个只出现一次的字符/README.md

@@ -193,6 +193,29 @@ public class Solution {
 }
 ```
 
+#### Swift
+
+```swift
+class Solution {
+    func firstUniqChar(_ s: String) -> Character {
+        var count = [Int](repeating: 0, count: 26)
+        let aAsciiValue = Int(Character("a").asciiValue!)
+
+        for char in s {
+            count[Int(char.asciiValue!) - aAsciiValue] += 1
+        }
+
+        for char in s {
+            if count[Int(char.asciiValue!) - aAsciiValue] == 1 {
+                return char
+            }
+        }
+
+        return " "
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- solution:end -->

lcof/面试题50. 第一个只出现一次的字符/Solution.swift

@@ -0,0 +1,18 @@
+class Solution {
+    func firstUniqChar(_ s: String) -> Character {
+        var count = [Int](repeating: 0, count: 26)
+        let aAsciiValue = Int(Character("a").asciiValue!)
+        
+        for char in s {
+            count[Int(char.asciiValue!) - aAsciiValue] += 1
+        }
+        
+        for char in s {
+            if count[Int(char.asciiValue!) - aAsciiValue] == 1 {
+                return char
+            }
+        }
+        
+        return " "
+    }
+}