🎉 feat: initial commit for leetcode 20 using Swift

Author: liuchuo

Swift/20. Valid Parentheses.swift

@@ -0,0 +1,22 @@
+// 20. Valid Parentheses
+// 16 ms, 74.38%
+func isValid(_ s: String) -> Bool {
+    var stack = [Character](), b = true
+
+    func compare(_ c: Character) -> Bool {
+        guard let t = stack.popLast()  else { return false }
+        return (c == ")" && t == "(") || (c == "]" && t == "[" ) || (c == "}" && t == "{")
+    }
+
+    loop: for c in s {
+        switch c {
+        case "(", "[", "{":
+            stack.append(c)
+        default:
+            b = compare(c)
+            if !b { break loop }
+        }
+    }
+    
+    return b && stack.isEmpty
+}