Create Sliding Window Maximum.cpp (#348)

Please approve my pr and add hacktoberfest label on it.

Author: sumitkr2000

CPP/sliding-window/Sliding Window Maximum.cpp

@@ -0,0 +1,35 @@
+class Solution {
+public:
+    vector<int> maxSlidingWindow(vector<int>& nums, int k) {
+        
+        deque<int> maxi(k);
+        vector<int> ans;
+        
+        for(int i = 0; i < k; i++) {
+
+            while(!maxi.empty() && nums[maxi.back()] <= nums[i]) {
+                maxi.pop_back();
+            }
+            maxi.push_back(i);
+        }
+        ans.push_back(nums[maxi.front()]);
+        
+        for(int i = k; i < nums.size(); i++) {
+
+            //removal
+            while(!maxi.empty() && i-maxi.front() >= k) {
+                maxi.pop_front();
+            }
+            
+            //addition
+            while(!maxi.empty() && nums[maxi.back()] <= nums[i]) {
+                maxi.pop_back();
+            }
+
+            maxi.push_back(i);
+
+            ans.push_back(nums[maxi.front()]);
+        }
+        return ans;
+    }
+};