[Array] add Solution to Sliding Window Maximum

Author: Yi Gu

Array/SlidingWindowMaximum.swift

@@ -0,0 +1,32 @@
+/**
+ * Question Link: https://leetcode.com/problems/sliding-window-maximum/
+ * Primary idea: Use an array to store indices of elements, from larger to smaller, 
+ *               adjust it while iterating the array
+ *
+ * Time Complexity: O(n), Space Complexity: O(n)
+ *
+ */
+
+class SlidingWindowMaximum {
+    func maxSlidingWindow(nums: [Int], _ k: Int) -> [Int] {
+        var maxIdx = [Int]()
+        var res = [Int]()
+        
+        for i in 0 ..< nums.count {
+            while maxIdx.count > 0 && nums[maxIdx.last!] < nums[i] {
+                maxIdx.removeLast()
+            }
+            
+            maxIdx.append(i)
+            
+            if i + 1 >= k {
+                res.append(nums[maxIdx.first!])
+            }
+            if i - maxIdx.first! + 1 == k {
+                maxIdx.removeFirst()
+            }
+        }
+        
+        return res
+    }
+}