Added new solutions

Author: Michael-Ho-Bose

0003-LongestSubstringWithoutRepeatingCharacters.playground/Contents.swift

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+// LeetCode: https://leetcode.com/problems/longest-substring-without-repeating-characters/description/
+
+class Solution {
+    func lengthOfLongestSubstring(_ s: String) -> Int {
+        guard s.count > 0 else {
+            return 0
+        }
+        
+        var maxCount = 1
+        if s.count == 1 {
+            return maxCount
+        }
+        let strArr = Array(s) // Key: convert string to array
+        for (index, char) in strArr.enumerated() {
+            var dict: [Character : Int] = [:]
+            var count = 1
+            dict[char] = 1
+            var movingIdx = index + 1
+            while movingIdx < strArr.count, dict[strArr[movingIdx]] ?? 0 < 1 {
+                dict[strArr[movingIdx]] = 1
+                count += 1
+                movingIdx += 1
+            }
+            maxCount = count > maxCount ? count : maxCount
+        }
+        return maxCount
+    }
+}
+
+let s = Solution()
+print("\(s.lengthOfLongestSubstring("dvdf"))")

0003-LongestSubstringWithoutRepeatingCharacters.playground/contents.xcplayground

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+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<playground version='5.0' target-platform='macos'>
+    <timeline fileName='timeline.xctimeline'/>
+</playground>

0006-ZigZagConversion.playground/Contents.swift

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+// LeetCode: https://leetcode.com/problems/zigzag-conversion/description/
+
+class Solution {
+    func convert(_ s: String, _ numRows: Int) -> String {
+        var output = ""
+        let divide = 2 * numRows - 2
+        guard divide > 1 else {
+            return s
+        }
+        var dict: [Int:String] = [:]
+        
+        for (index, char) in s.enumerated() {
+            let dictIdx = (index % divide) < numRows ? (index % divide) + 1 : numRows - ((index % divide) + 1 - numRows)
+            if nil != dict[dictIdx] {
+                dict[dictIdx]!.append(char)
+            } else {
+                dict[dictIdx] = String(char)
+            }
+        }
+        for i in 1...dict.count {
+            output.append(dict[i]!)
+        }
+        return output
+    }
+}
+
+let solution = Solution()
+print("\(solution.convert("PAYPALISHIRING", 3))")
+print("\(solution.convert("PAYPALISHIRING", 4))")

0006-ZigZagConversion.playground/contents.xcplayground

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+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<playground version='5.0' target-platform='macos'>
+    <timeline fileName='timeline.xctimeline'/>
+</playground>

0206-ReverseLinkedList.playground/Contents.swift

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+// LeetCode: https://leetcode.com/problems/reverse-linked-list/description/
+
+public class ListNode {
+    public var val: Int
+    public var next: ListNode?
+    public init(_ val: Int) {
+        self.val = val
+        self.next = nil
+    }
+    
+    public init(_ val: Int, _ next: ListNode?) {
+        self.val = val
+        self.next = next
+    }
+}
+
+class Solution {
+    func reverseList(_ head: ListNode?) -> ListNode? {
+        guard let head = head else {
+            return nil
+        }
+        var currentNode: ListNode? = head
+        var prev: ListNode? = nil // The previous node of head is nil
+        while nil != currentNode {
+            let next: ListNode? = currentNode?.next
+            currentNode?.next = prev
+            prev = currentNode
+            currentNode = next
+        }
+        return prev
+    }
+    
+    func printLinkedList(_ head: ListNode) {
+        var printedStr = ""
+        var currentNode: ListNode? = head
+        while nil != currentNode {
+            printedStr.append("\(currentNode?.val ?? -1)")
+            if nil != currentNode?.next {
+                printedStr.append(", ")
+            }
+            currentNode = currentNode?.next
+        }
+        print(printedStr)
+    }
+}
+
+let solution = Solution()
+let node5 = ListNode(5, nil)
+let node4 = ListNode(4, node5)
+let node3 = ListNode(3, node4)
+let node2 = ListNode(2, node3)
+let node1 = ListNode(1, node2)
+solution.printLinkedList(node1)
+
+// Reverse Linked List
+print("Reversed below:")
+solution.printLinkedList(solution.reverseList(node1)!)

0206-ReverseLinkedList.playground/contents.xcplayground

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+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<playground version='5.0' target-platform='macos'>
+    <timeline fileName='timeline.xctimeline'/>
+</playground>