227. Basic Calculator II

Author: partho-maple

README.md

@@ -331,6 +331,7 @@ I have solved quite a number of problems from several topics. See the below tabl
 |17| **[636. Exclusive Time of Functions](https://tinyurl.com/y7fkfomp)** | [Python](https://tinyurl.com/wu6rdaw/636_Exclusive_Time_of_Functions.py), [Swift](https://tinyurl.com/wuja3c4/636_Exclusive_Time_of_Functions.swift)| [Art 1](https://tinyurl.com/yd5rtdkl) | Medium | Must check |
 |18| **[921. Minimum Add to Make Parentheses Valid](https://tinyurl.com/wjv6txp)** | [Python](https://tinyurl.com/wu6rdaw/921_Minimum_Add_to_Make_Parentheses_Valid.py), [Swift](https://tinyurl.com/wuja3c4/921_Minimum_Add_to_Make_Parentheses_Valid.swift)| --- | Medium | --- |
 |19| **[1209. Remove All Adjacent Duplicates in String II](https://tinyurl.com/y3e4gsgv)** | [Python](https://tinyurl.com/wu6rdaw/1209_Remove_All_Adjacent_Duplicates_in_String_II.py), [Swift](https://tinyurl.com/wuja3c4/1209_Remove_All_Adjacent_Duplicates_in_String_II.swift)| --- | Medium | --- |
+|20| **[227. Basic Calculator II](https://tinyurl.com/y5g4u5by)** | [Python](https://tinyurl.com/wu6rdaw/227_Basic_Calculator_II.py), [Swift](https://tinyurl.com/wuja3c4/227_Basic_Calculator_II.swift)| [Art 1](https://tinyurl.com/y3dnn3zl) | Medium | --- |
 
 </p>
 </details>

leetcode.com/swift/DS_ALGO_PRAC.playground/Sources/swift/227_Basic_Calculator_II.swift

@@ -0,0 +1,28 @@
+import Foundation
+class Solution {
+    func calculate(_ s: String) -> Int {
+        var expression: [String] = Array(s).map { String($0) }.filter { $0 != " " }
+        var (stack, currentSign, rightNum) = ([Int](), "+", 0)
+        for (index, value) in expression.enumerated() {
+            if let num = Int(value) {
+                rightNum = rightNum * 10 + num
+            }
+            if (index == expression.count - 1) || ["+", "-", "*", "/"].contains(value) {
+                if currentSign == "+" {
+                    stack.append(rightNum)
+                } else if currentSign == "-" {
+                    stack.append(0 - rightNum)
+                } else if currentSign == "*" {
+                    let leftNum = stack.popLast()!
+                    stack.append(leftNum * rightNum)
+                } else {
+                    let leftNum = stack.popLast()!
+                    stack.append(leftNum / rightNum)
+                }
+                currentSign = value
+                rightNum = 0
+            }
+        }
+        return stack.reduce(0) { $0 + $1 }
+    }
+}