spurscho

class Solution {
    func swapPairs(_ head: ListNode?) -> ListNode? {
        guard let newHead = head?.next else {
            return head
        }
        // 1 -> 2 -> 3 -> 4
        // 2 -> 1 -> 4 -> 3
        let tmp = head?.next?.next
        head?.next?.next = head
        head?.next = swapPairs(tmp)

spurscho

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     public var val: Int
 *     public var next: ListNode?
 *     public init(_ val: Int) {
 *         self.val = val
 *         self.next = nil
 *     }
 * }

spurscho

class Solution {
    func generateParenthesis(_ n: Int) -> [String] {
        var result = [String]()
        if(n == 0) {
            return result
        }
        var str = ""
        generateParenthesisUtil(&result,str,n,0,0)
        return result
    }

spurscho

class Solution {
    func threeSum(_ nums: [Int]) -> [[Int]] {
        var nums = nums; nums.sort()
        var result = [[Int]]()
        guard nums.count >= 3 else {return result}
        //i,l,r indices
        for i in 0..<nums.count-2{
            if(i > 0 && nums[i] == nums[i-1]) {continue}
            var l=i+1, r=nums.count-1
            var targetValue = nums[i]

spurscho

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     public var val: Int
 *     public var next: ListNode?
 *     public init(_ val: Int) {
 *         self.val = val
 *         self.next = nil
 *     }
 * }

spurscho

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     public var val: Int
 *     public var next: ListNode?
 *     public init(_ val: Int) {
 *         self.val = val
 *         self.next = nil
 *     }
 * }

spurscho

import UIKit

class Node {
    let value: Int
    var next: Node?
    
    init(_ value:Int, _ next: Node?) {
        self.value = value
        self.next = next
    }

spurscho

class Solution {
    let phoneDict: [Int : String] = [
        2 : "abc",
        3 : "def",
        4 : "ghi",
        5 : "jkl",
        6 : "mno",
        7 : "pqrs",
        8 : "tuv",
        9 : "wxyz"

spurscho

class Solution {
    func isValid(_ s: String) -> Bool {
        var stack = [Character]()
        let closingPairs: [Character:Character] = [ "{":"}", "[":"]", "(":")" ]
        let openBrackets = Set<Character>(closingPairs.keys)
        for char in s {
            if openBrackets.contains(char) {
                stack.append(char)
            } else {
                guard let last = stack.popLast() else {

spurscho

var p1: ListNode? = l1
        var p2: ListNode? = l2
        
        var resultNode: ListNode? = ListNode(0)
        let head = resultNode
        var carry = 0
        while p1 != nil || p2 != nil || carry > 0 {
            let val1 = p1?.val ?? 0
            let val2 = p2?.val ?? 0
            let sum = val1 + val2 + carry