Modified 0020-valid-parentheses.swift for better readability and understanding

swift/0020-valid-parentheses.swift

@@ -1,47 +1,23 @@
 class Solution {
+    // Input: s = "()[]{}"
     func isValid(_ s: String) -> Bool {
-        let parenMap:[Character:Character] = ["(":")", "[":"]", "{":"}"]
-        var stack = Stack<Character>()
-        for c in s {
-            if parenMap.keys.contains(c) {
-                stack.push(c)
-            } else if stack.isEmpty || c != parenMap[stack.pop()!] {
-                return false
+         let closeToOpenDic: [Character:Character] = [
+        "}": "{",
+        ")": "(",
+        "]": "["]
+          var stack = [Character]()
+        for char in s {
+            for char in s {
+                let c = closeToOpenDic[char]
+                if c == nil {
+                    stack.append(char)
+                }else{
+                    if stack.popLast() != c {
+                        return false
+                    }
+                }
             }
         }
-        return stack.isEmpty
-    }
-}
-
-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
+        return stack.count == 0
     }
 }