adding a sliding window problem

leetcode/p643_max_average_subarray.cpp

@@ -0,0 +1,28 @@
+// sliding window problem.
+// O(n) solution
+class Solution {
+public:
+    double findMaxAverage(vector<int>& nums, int k) {
+        double result = INT_MIN;
+        double sum = 0.00;
+        int size = nums.size();
+        int low = 0;
+        int high = 0;
+        while(high<size){
+            sum += nums[high];
+            if(high-low+1 == k){
+                if(sum > result){
+                    result = sum;
+                }
+                // always make sure there are no more than k elements in this sum.
+                sum -= nums[low];
+                // slide the window
+                low++;
+            }
+            // slide the window
+            high++;
+        }
+        result = result/k;
+        return result;
+    }
+};