human
Give me a Python code to calculate the sum of all possible odd-length subarrays given the following:
Solve in Python:
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
assistant
#Here is Python code to calculate the sum of all possible odd-length subarrays.

class Solution:
    def sumOddLengthSubarrays(self, arr: List[int]) -> int:
        cur_sum, prefix_sum = 0, [0] * (len(arr) + 1)
        ret = 0
        for i in range(1, len(arr)+1):
            cur_sum += arr[i-1]
            prefix_sum[i] = cur_sum
            for j in range(1, i+1, 2):
                # print([i, j])
                ret += prefix_sum[i] - prefix_sum[i-j]
        return ret