[Array] Add a solution to Asteroid Collision

Author: soapyigu

Array/AsteroidCollision.swift

@@ -0,0 +1,42 @@
+/**
+ * Question Link: https://leetcode.com/problems/asteroid-collision/
+ * Primary idea: traverse the array and handle positive and negative separately
+ *
+ * Time Complexity: O(n), Space Complexity: O(n)
+ *
+ */
+
+class AsteroidCollision {
+    func asteroidCollision(_ asteroids: [Int]) -> [Int] {
+        var positives = [Int]()
+        var negatives = [Int]()
+        
+        for asteroid in asteroids {
+            if asteroid > 0 {
+                positives.append(asteroid)
+            } else {
+                var shouldAppendToNegative = true
+                
+                while positives.count > 0 {
+                    if positives.last! > -asteroid {
+                        shouldAppendToNegative = false
+                        break
+                    } else {
+                        let last = positives.removeLast()
+                        
+                        if -asteroid == last {
+                            shouldAppendToNegative = false
+                            break
+                        }
+                    }
+                }
+                
+                if shouldAppendToNegative {
+                    negatives.append(asteroid)
+                }
+            }
+        }
+        
+        return negatives + positives
+    }
+}

README.md

@@ -28,7 +28,7 @@
 * [Microsoft](#microsoft)
 
 ## Progress
-[Problem Status](#problem-status) shows the latest progress to all 800+ questions. Currently we have 256 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 257 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
@@ -54,6 +54,7 @@
 [3Sum Closest](https://leetcode.com/problems/3sum-closest/)| [Swift](./Array/ThreeSum.swift)| Medium| O(n^2)| O(nC3)|
 [4Sum](https://leetcode.com/problems/4sum/)| [Swift](./Array/FourSum.swift)| Medium| O(n^3)| O(nC4)|
 [Summary Ranges](https://leetcode.com/problems/summary-ranges/)| [Swift](./Array/SummaryRanges.swift)| Medium| O(n)| O(n)|
+[Asteroid Collision](https://leetcode.com/problems/asteroid-collision/)| [Swift](./Array/AsteroidCollision.swift)| Medium| O(n)| O(n)|
 [Shortest Word Distance](https://leetcode.com/problems/shortest-word-distance/)| [Swift](./Array/ShortestWordDistance.swift)| Easy| O(n)| O(1)|
 [Shortest Word Distance III](https://leetcode.com/problems/shortest-word-distance-iii/)| [Swift](./Array/ShortestWordDistanceIII.swift)| Medium| O(n)| O(1)|
 [Minimum Size Subarray Sum](https://leetcode.com/problems/minimum-size-subarray-sum/)| [Swift](./Array/MinimumSizeSubarraySum.swift)| Medium| O(n)| O(1)|