davidseek

class RandomizedSet {
    
    private var data: Set<Int> = []
  
    /** 
    Inserts a value to the set. 
    Returns true if the set did not already 
    contain the specified element.
    */
    func insert(_ val: Int) -> Bool {

davidseek

func isPowerOfTwo(_ n: Int) -> Bool {

    // 1    
    guard n != 1 && n != 2 else {
        return true
    }

    // 2
    var last: Int = 2

davidseek

func levelOrder(_ root: TreeNode?) -> [[Int]] {     
      
    // 1  
    guard let root = root else {
        return []
    }

    // 2
    var queue = Queue()
    

davidseek

struct Queue {
    
    typealias NodeAtLevel = (node: TreeNode, level: Int)
    
    private var enqueueStack: [NodeAtLevel] = []
    private var dequeueStack: [NodeAtLevel] = []
    
    public var isEmpty: Bool {
        return enqueueStack.isEmpty && dequeueStack.isEmpty
    }

davidseek

func reverseString(_ s: inout [Character]) {
    s = s.reversed()
}

davidseek

func reverseString(_ s: inout [Character]) {
    s.reverse()
}

davidseek

func reverseString(_ s: inout [Character]) {
        
    // Call our recursive helper function
    swapCharacters(
        atLeftPointer: 0,
        andRightPointer: s.count - 1,
        in: &s
    )
}
    

davidseek

func deleteNode(_ node: ListNode?) {

    // First we assign next's .value 
    node?.val = node?.next?.val ?? Int()
    
    // And then next's .next
    node?.next = node?.next?.next    
}

davidseek

func addTwoNumbers(_ l1: ListNode?, _ l2: ListNode?) -> ListNode? {
        
    // Get a mutable reference to each head of l1 and l2
    var currentL1: ListNode? = l1
    var currentL2: ListNode? = l2

    // Create a reference to a node we're going to append on
    var sumList: ListNode? = ListNode(-1)

    // And a reference to its head

davidseek

func twoSum(_ nums: [Int], _ target: Int) -> [Int] {
    /**
    Init an empty dictionary.
    The value will be the array element.
    The key will be the index of the element.
    */
    var hashMap: [Int: Int] = [:]
    // Iterate through every element in numbers
    for (i, element) in numbers.enumerated() {