feat: add swift implementation to lcof problem: No.10.2 (#2857)

Author: klever34

Diff for: lcof/面试题10- II. 青蛙跳台阶问题/README.md

@@ -174,6 +174,25 @@ public class Solution {
 }
 ```
 
+#### Swift
+
+```swift
+class Solution {
+    func numWays(_ n: Int) -> Int {
+        var a = 1
+        var b = 1
+        var count = n
+        while count > 0 {
+            let c = (a + b) % 1000000007
+            a = b
+            b = c
+            count -= 1
+        }
+        return a
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- solution:end -->

Diff for: lcof/面试题10- II. 青蛙跳台阶问题/Solution.swift

@@ -0,0 +1,14 @@
+class Solution {
+    func numWays(_ n: Int) -> Int {
+        var a = 1
+        var b = 1
+        var count = n
+        while count > 0 {
+            let c = (a + b) % 1000000007
+            a = b
+            b = c
+            count -= 1
+        }
+        return a
+    }
+}