     var stack = Stacky<Character>(items: Array(word.characters))
     var reverseStack = Stacky<Character>(items: Array(word.characters).reverse())
     
-    for _ in 0..<stack.count() {
-        if stack.pop() != reverseStack.pop() {
+    for _ in 0..<stack.count() { // O(n)
+        if stack.pop() != reverseStack.pop() { // O(1)
             return false
         }
     }

    
    return sum
}
powerOfN(2, power: 4)
powerOfN(0, power: 4) // 0
powerOfN(1, power: 4) // 1
powerOfN(2, power: 1) // 2
powerOfN(2, power: 0) // 1














// check array for missing number in consecutive numbers, return that number (to reuse numbers)

// assign that number to a customer


// take in string, return letter that appears the most frequently
//func mostCommonLetter(word: String) -> String? {
//    
//    var tracker: Dictionary<String,Int> = [:]
//    
//    var count: Int = 1
//    let wordArray = word.characters.map {String($0)} // convert to array of strings
//    
//    var letter: String? = nil
//    var largestNumber = 0
//    
//    for letter in wordArray {
//        
//        if !tracker.keys.contains(letter) {
//            tracker[letter] = count
//        } else {
//            
//        }
//  
//    }
//    
//    print(tracker)
//
//    return letter
//}
//    
//
//mostCommonLetter("heellloe")



//adding / multiplying / traversing multi dimensional arrays
//caesar cypher
//tic tac toe
//Check to see if string is balanced (())
//Given three numbers return the median
//Fibonacci - given an idx return the fib value at idx
//given a jumble: String and knownWords: [String] return list of potential words that the string may be.

addValues(arr2)


// create function that determines n to the power of n
func powerOfN(number: Int, power: Int) -> Int {
    var sum = 1
    
    if power == 0 { // O(1)
        return 1
    }
    
