         
         return false
     }
-    //MARK - 43. Multiply Strings
+    //MARK: - 43. Multiply Strings
     func multiply(_ num1: String, _ num2: String) -> String {
         if num1 == "0" || num2 == "0" {
             return "0"

        head.next = l1 != nil ? l1 : l2
        return result.next
    }
    //MARK - 231. Power of Two
    func isPowerOfTwo(_ n: Int) -> Bool {
        return n > 0 && (n & (n - 1) == 0)
    }

        }
        return result;
    }
    //MARK: - 322. Coin Change
    func coinChange(_ coins: [Int], _ amount: Int) -> Int {
        if amount == 0 {
            return 0
        }
        let len = coins.count
        var nums:[Int] = Array.init(repeating: Int.max - 1, count: amount + 1)
        for i in 0 ..< len {
            if coins[i] <= amount {
                nums[coins[i]] = 1
