Added solutions for 1, 2, 4, 7, 69

Author: Michael-Ho-Bose

0001-TwoSum.playground/Contents.swift

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+// LeetCode: https://leetcode.com/problems/two-sum/description/
+// Solution: https://github.com/zhubofei/LeetCode-Swift/blob/master/0001-two-sum.playground/Contents.swift
+
+func twoSum(_ nums: [Int], _ target: Int) -> [Int] {
+    var dict: [Int: Int] = [:] // [number : indexPosition]
+    for (index, num) in nums.enumerated() {
+        let complement = target - num
+        if let compIndex = dict[complement] {
+            return [index, compIndex]
+        }
+        dict[num] = index
+    }
+    fatalError()
+}

0001-TwoSum.playground/contents.xcplayground

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

0002-AddTwoNumbers.playground/Contents.swift

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+// LeetCode: https://leetcode.com/problems/add-two-numbers/description/
+// Solution: https://github.com/zhubofei/LeetCode-Swift/blob/master/0002-add-two-numbers.playground/Contents.swift
+
+import Foundation
+
+public class ListNode {
+    public var val: Int
+    public var next: ListNode?
+    public init(_ val: Int) {
+        self.val = val
+        self.next = nil
+    }
+}
+
+class Solution {
+    func addTwoNumbers(_ l1: ListNode?, _ l2: ListNode?) -> ListNode? {
+        guard let l1 = l1, let l2 = l2 else {
+            fatalError()
+        }
+        if l1.next == nil, l2.next == nil {
+            let node = ListNode((l1.val + l2.val) % 10)
+            if l1.val + l2.val >= 10 {
+                node.next = ListNode(1)
+            }
+            return node
+        }
+        var node1: ListNode? = l1
+        var node2: ListNode? = l2
+        var temp = ListNode((l1.val + l2.val) % 10)
+        let head = temp
+        var shouldAdd: Bool = ((l1.val + l2.val) / 10) > 0
+        
+        while nil != node1?.next || nil != node2?.next || shouldAdd {
+            var val1 = 0
+            var val2 = 0
+            if let node = node1?.next {
+                val1 = node.val
+                node1 = node
+            }
+            
+            if let node = node2?.next {
+                val2 = node.val
+                node2 = node
+            }
+            
+            let newValue = (val1 + val2 + (shouldAdd ? 1 : 0)) % 10
+            shouldAdd = (val1 + val2) + (shouldAdd ? 1 : 0) >= 10
+            
+            temp.next = ListNode(newValue)
+            temp = temp.next! 
+        }
+        return head
+    }
+}

0002-AddTwoNumbers.playground/contents.xcplayground

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

0004-MedianOfTwoSortedArrays.playground/Contents.swift

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+// LeetCode: https://leetcode.com/problems/median-of-two-sorted-arrays/description/
+// Hint: merge sort
+
+class Solution {
+    func findMedianSortedArrays(_ nums1: [Int], _ nums2: [Int]) -> Double {
+        var leftIndex = 0
+        var rightIndex = 0
+        var results: [Int] = []
+        
+        var shouldSort = true
+        while shouldSort {
+            if leftIndex >= nums1.count {
+                results.append(contentsOf: Array(nums2[rightIndex..<nums2.count]))
+                shouldSort = false
+                break
+            }
+            
+            if rightIndex >= nums2.count {
+                results.append(contentsOf: Array(nums1[leftIndex..<nums1.count]))
+                shouldSort = false
+                break
+            }
+            
+            if nums1[leftIndex] > nums2[rightIndex] {
+                results.append(nums2[rightIndex])
+                rightIndex += 1
+            } else {
+                results.append(nums1[leftIndex])
+                leftIndex += 1
+            }
+        }
+        
+        if results.count % 2 == 0 {
+            return Double(results[results.count/2 - 1] + results[results.count/2])/2
+        } else {
+            return Double(results[results.count/2])
+        }
+    }
+}
+
+// Test
+let solution = Solution()
+print("\(solution.findMedianSortedArrays([1, 3], [2, 4]))")
+print("\(solution.findMedianSortedArrays([1, 3], [2]))")

0004-MedianOfTwoSortedArrays.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>

0007-ReverseInteger+0069-Sqrtx.playground/Contents.swift

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+// LeetCode: https://leetcode.com/problems/reverse-integer/description/
+import Foundation
+
+class Solution {
+    func reverse(_ x: Int) -> Int {
+        var temp = abs(x)
+        var output = 0
+        while temp > 0 {
+            var tail = temp % 10
+            temp = temp / 10
+            output = output * 10 + tail
+            if (output > Int32.max || output < Int32.min) { return 0 }
+        }
+        
+        return output * x.signum() // Times back the sign of the original number
+    }
+    
+    func mySqrt(_ x: Int) -> Int {
+        return Int(sqrt(Double(x)))
+        
+    }
+}
+
+let solution = Solution()
+print("\(solution.reverse(-123))")
+print("\(solution.mySqrt(8))")

0007-ReverseInteger+0069-Sqrtx.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>