feat: add swift solution2 implementation to lcof2 problem: No.088 (doocs#3474)

Author: klever34

lcof2/剑指 Offer II 088. 爬楼梯的最少成本/README.md

@@ -235,6 +235,23 @@ function minCostClimbingStairs(cost: number[]): number {
 }
 ```
 
+#### Swift
+
+```swift
+class Solution {
+    func minCostClimbingStairs(_ cost: [Int]) -> Int {
+        var a = 0
+        var b = 0
+        for i in 1..<cost.count {
+            let c = min(a + cost[i - 1], b + cost[i])
+            a = b
+            b = c
+        }
+        return b
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- solution:end -->

lcof2/剑指 Offer II 088. 爬楼梯的最少成本/Solution2.swift

@@ -0,0 +1,12 @@
+class Solution {
+    func minCostClimbingStairs(_ cost: [Int]) -> Int {
+        var a = 0
+        var b = 0
+        for i in 1..<cost.count {
+            let c = min(a + cost[i - 1], b + cost[i])
+            a = b
+            b = c
+        }
+        return b
+    }
+}