[Array] Add a solution to First Missing Positive

Author: soapyigu

Array/FirstMissingPositive.swift

@@ -0,0 +1,22 @@
+/**
+ * Question Link: https://leetcode.com/problems/first-missing-positive/
+ * Primary idea: Use a set to hold number in the array and iterate through 1...nums.count to find the missing one
+ * Time Complexity: O(n), Space Complexity: O(n)
+ *
+ */
+
+class FirstMissingPositive {
+    func firstMissingPositive(_ nums: [Int]) -> Int {
+        var set = Set<Int>()
+        
+        nums.forEach { set.insert($0) }
+        
+        for i in 0..<nums.count {
+            if !set.contains(i + 1) {
+                return i + 1
+            }
+        }
+        
+        return nums.count + 1
+    }
+}

README.md

@@ -28,7 +28,7 @@
 * [Microsoft](#microsoft)
 
 ## Progress
-[Problem Status](#problem-status) shows the latest progress to all 800+ questions. Currently we have 269 completed solutions. Note: questions with ♥ mark means that you have to **Subscript to premium membership** of LeetCode to unlock them. Thank you for great contributions from [CharleneJiang](https://github.com/CharleneJiang), [ReadmeCritic](https://github.com/ReadmeCritic), [demonkoo](https://github.com/demonkoo), [DaiYue](https://github.com/DaiYue), [Quaggie](https://github.com/Quaggie) and [jindulys](https://github.com/jindulys).
+[Problem Status](#problem-status) shows the latest progress to all 800+ questions. Currently we have 270 completed solutions. Note: questions with ♥ mark means that you have to **Subscript to premium membership** of LeetCode to unlock them. Thank you for great contributions from [CharleneJiang](https://github.com/CharleneJiang), [ReadmeCritic](https://github.com/ReadmeCritic), [demonkoo](https://github.com/demonkoo), [DaiYue](https://github.com/DaiYue), [Quaggie](https://github.com/Quaggie) and [jindulys](https://github.com/jindulys).
 
 
 ## Array
@@ -40,6 +40,7 @@
 [Island Perimeter](https://leetcode.com/problems/island-perimeter/)| [Swift](./Array/IslandPerimeter.swift)| Easy| O(nm)| O(1)|
 [Majority Element](https://leetcode.com/problems/majority-element/)| [Swift](./Array/MajorityElement.swift)| Easy| O(n)| O(1)|
 [Majority Element II](https://leetcode.com/problems/majority-element-ii/)| [Swift](./Array/MajorityElementII.swift)| Medium| O(n)| O(1)|
+[First Missing Positive](https://leetcode.com/problems/first-missing-positive/)| [Swift](./Array/FirstMissingPositive.swift)| Hard| O(n)| O(n)|
 [Intersection of Two Arrays](https://leetcode.com/problems/intersection-of-two-arrays/)| [Swift](./Array/IntersectionTwoArrays.swift)| Easy| O(n)| O(n)|
 [Intersection of Two Arrays II](https://leetcode.com/problems/intersection-of-two-arrays-ii/)| [Swift](./Array/IntersectionTwoArraysII.swift)| Easy| O(n)| O(n)|
 [Contains Duplicate](https://leetcode.com/problems/contains-duplicate/)| [Swift](./Array/ContainsDuplicate.swift)| Easy| O(n)| O(n)|
@@ -787,7 +788,7 @@
 |	[Swift](./DP/WildcardMatching.swift)	|	44	|	[Wildcard Matching](https://oj.leetcode.com/problems/wildcard-matching/)	| Hard	|
 |	[Swift](./String/MultiplyStrings.swift)	|	43	|	[Multiply Strings](https://oj.leetcode.com/problems/multiply-strings/)	| Medium	|
 |	[Swift](./Math/TrappingRainWater.swift)	|	42	|	[Trapping Rain Water](https://oj.leetcode.com/problems/trapping-rain-water/)	| Hard	|
-|		|	41	|	[First Missing Positive](https://oj.leetcode.com/problems/first-missing-positive/)	| Hard	|
+|	[Swift](./Array/FirstMissingPositive.swift)	|	41	|	[First Missing Positive](https://oj.leetcode.com/problems/first-missing-positive/)	| Hard	|
 |	[Swift](./DFS/combinationSumII.swiftc)	|	40	|	[Combination Sum II](https://oj.leetcode.com/problems/combination-sum-ii/)	| Medium	|
 |	[Swift](./DFS/CombinationSum.swift)	|	39	|	[Combination Sum](https://oj.leetcode.com/problems/combination-sum/)	| Medium	|
 |	[Swift](./String/CountAndSay.swift)	|	38	|	[Count and Say](https://oj.leetcode.com/problems/count-and-say/)	| Easy	|