1588. Sum of All Odd Length Subarrays.cpp

Given an array of positive integers arr, calculate the sum of all possible odd-length subarrays.

A subarray is a contiguous subsequence of the array.

Return the sum of all odd-length subarrays of arr.



Example 1:

Input: arr = [1,4,2,5,3]
Output: 58
Explanation: The odd-length subarrays of arr and their sums are:
[1] = 1
[4] = 4
[2] = 2
[5] = 5
[3] = 3
[1,4,2] = 7
[4,2,5] = 11
[2,5,3] = 10
[1,4,2,5,3] = 15
If we add all these together we get 1 + 4 + 2 + 5 + 3 + 7 + 11 + 10 + 15 = 58
Example 2:

Input: arr = [1,2]
Output: 3
Explanation: There are only 2 subarrays of odd length, [1] and [2]. Their sum is 3.
Example 3:

Input: arr = [10,11,12]
Output: 66


Constraints:

1 <= arr.length <= 100
1 <= arr[i] <= 1000








class Solution {
public:
    int sumOddLengthSubarrays(vector<int>& arr) {
        int sum=0;

        int n=arr.size();

        for(int len=1; len<=n; len+=2){
            int fsum=0;

            for(int i=0;i<len;i++){
                fsum+=arr[i];
            }

            sum+=fsum;


            for(int i=1;i<=n-len;i++){
                fsum=fsum-arr[i-1]+arr[len+i-1];
                sum+=fsum;
            }
        }
        return sum;
    }
};