added solution

1501-1600/1588. Sum of All Odd Length Subarrays/1588.cpp

@@ -0,0 +1,16 @@
+class Solution {
+public:
+    int sumOddLengthSubarrays(vector<int>& arr) {
+       // contribution of each element in subarrrays = (i+1) * (n-i) 
+        // i.e, hoe many left indexes for start (including a[i]) * how many right indexes to end ( including a[i])
+        // for odd length, just divide by 2
+        // now, we have element and it's contribution number, add number * contribution to your answer
+        int ans =0,n=arr.size();
+        for(int i =0;i<n;i++)
+		{
+            int contribution = ceil((i+1)*(n-i)/2.0);
+            ans+=(contribution*arr[i]);
+        }
+        return ans;
+    }
+};