feat: add swift implementation to lcof2 problem: No.036 (doocs#3041)

Author: klever34

lcof2/剑指 Offer II 036. 后缀表达式/README.md

@@ -217,6 +217,37 @@ func popInt(stack *arraystack.Stack) int {
 }
 ```
 
+#### Swift
+
+```swift
+class Solution {
+    func evalRPN(_ tokens: [String]) -> Int {
+        var stk = [Int]()
+
+        for token in tokens {
+            if let num = Int(token) {
+                stk.append(num)
+            } else {
+                let y = stk.removeLast()
+                let x = stk.removeLast()
+                switch token {
+                case "+":
+                    stk.append(x + y)
+                case "-":
+                    stk.append(x - y)
+                case "*":
+                    stk.append(x * y)
+                default:
+                    stk.append(x / y)
+                }
+            }
+        }
+
+        return stk.removeLast()
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- solution:end -->

lcof2/剑指 Offer II 036. 后缀表达式/Solution.swift

@@ -0,0 +1,26 @@
+class Solution {
+    func evalRPN(_ tokens: [String]) -> Int {
+        var stk = [Int]()
+
+        for token in tokens {
+            if let num = Int(token) {
+                stk.append(num)
+            } else {
+                let y = stk.removeLast()
+                let x = stk.removeLast()
+                switch token {
+                case "+":
+                    stk.append(x + y)
+                case "-":
+                    stk.append(x - y)
+                case "*":
+                    stk.append(x * y)
+                default:
+                    stk.append(x / y)
+                }
+            }
+        }
+
+        return stk.removeLast()
+    }
+}