feat: add swift implementation to lcp problem: No.17 (doocs#3753)

Author: klever34

lcp/LCP 17. 速算机器人/README.md

@@ -118,6 +118,25 @@ func calculate(s string) int {
 }
 ```
 
+#### Swift
+
+```swift
+class Solution {
+    func calculate(_ s: String) -> Int {
+        var x = 1
+        var y = 0
+        for c in s {
+            if c == "A" {
+                x = x * 2 + y
+            } else if c == "B" {
+                y = y * 2 + x
+            }
+        }
+        return x + y
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- solution:end -->

lcp/LCP 17. 速算机器人/Solution.swift

@@ -0,0 +1,14 @@
+class Solution {
+    func calculate(_ s: String) -> Int {
+        var x = 1
+        var y = 0
+        for c in s {
+            if c == "A" {
+                x = x * 2 + y
+            } else if c == "B" {
+                y = y * 2 + x
+            }
+        }
+        return x + y
+    }
+}