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+import Foundation
+
+/*
+
+Week 135:
+
+    https://theweeklychallenge.org/blog/perl-weekly-challenge-135
+
+Task #1: Middle 3-digits
+
+    You are given an integer.
+
+    Write a script find out the middle 3-digits of the given integer, if possible otherwise throw sensible error.
+
+*/
+
+enum ParamError: Error {
+    case missingNum
+    case invalidNum
+    case tooShort
+    case evenNumberOfDigits
+}
+
+do {
+    let paramCount:Int = Int(CommandLine.argc)
+
+    if paramCount <= 1 {
+        throw ParamError.missingNum
+    }
+
+    let num:String = CommandLine.arguments[1]
+
+    if isValid(num) {
+
+        let n:Int    = abs(Int(num)!)
+        let s:String = String(n)
+        let l:Int    = s.count
+
+        if l == 1 {
+            throw ParamError.tooShort
+        }
+
+        if l % 2 == 0 {
+            throw ParamError.evenNumberOfDigits
+        }
+
+        let i:Int = (l / 2) - 1
+        let str:String = String(n)
+
+        let start = str.index(str.startIndex, offsetBy: i)
+        let end   = str.index(str.endIndex, offsetBy: 3 - (str.count-i))
+        let range = start..<end
+
+        print(str[range])
+
+    }
+    else {
+        throw ParamError.invalidNum
+    }
+}
+catch ParamError.missingNum {
+    print("Missing number.")
+}
+catch ParamError.invalidNum {
+    print("Invalid number.")
+}
+catch ParamError.tooShort {
+    print("Too short.")
+}
+catch ParamError.evenNumberOfDigits {
+    print("Even number of digits.")
+}
+catch let error {
+    print(error)
+}
+
+//
+//
+// Function
+
+func isValid(_ num:String) -> Bool {
+
+    let pattern = "^\\-?\\d+$"
+    let regex   = try! NSRegularExpression(pattern: pattern)
+    let range   = NSRange(location: 0, length: num.utf16.count)
+
+    if regex.firstMatch(in: num, options: [], range: range) != nil {
+        return true
+    }
+    else {
+        return false
+    }
+}