Merge pull request neetcode-gh#615 from diss1993/ticket/150

Swift | 150. Evaluate Reverse Polish Notation

Author: Ahmad-A0

swift/150-Evaluate-Reverse-Polish-Notation.swift

@@ -0,0 +1,58 @@
+class Solution {
+    func evalRPN(_ tokens: [String]) -> Int {
+        guard tokens.count > 0 else { return 0 }
+        var stack: Stack<Int> = Stack()
+        for c in tokens {
+            if c == "+" {
+                stack.push((stack.pop() ?? 0) + (stack.pop() ?? 0) )
+            } else if c == "-" {
+                var a = stack.pop() ?? 0
+                var b = stack.pop() ?? 0
+                stack.push(b - a)
+            } else if c == "*" {
+                stack.push((stack.pop() ?? 0) * (stack.pop() ?? 0) )
+            } else if c == "/" {
+                var a = stack.pop() ?? 0
+                var b = stack.pop() ?? 0
+                stack.push(b / a)
+            } else {
+                stack.push(Int(c) ?? 0)
+            }
+        }
+        return stack.pop() ?? 0
+    }
+}
+
+class Node<T> {
+    var data: T
+    var next: Node<T>?
+    init(_ value: T) {
+        self.data = value
+    }
+}
+
+class Stack<T> {
+
+    var head: Node<T>?
+
+    var isEmpty: Bool {
+        head == nil
+    }
+
+    func peak() -> Node<T>? {
+        head
+    }
+
+    func push(_ data: T) {
+        var node = Node<T>(data)
+        node.next = head
+        head = node
+    }
+
+    func pop() -> T? {
+        var data = head?.data
+        head = head?.next
+        return data
+    }
+
+}