# 1588. Sum of All Odd Length Subarrays

Easy
Given an array of positive integers `arr`, return the sum of all possible odd-length subarrays of `arr`.
A subarray is a contiguous subsequence of the array.
Example 1:
Input: arr = [1,4,2,5,3]
Output:
58
Explanation:
The odd-length subarrays of arr and their sums are:
 = 1
 = 4
 = 2
 = 5
 = 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,  and . Their sum is 3.
Example 3:
Input: arr = [10,11,12]
Output:
66
Constraints:
• `1 <= arr.length <= 100`
• `1 <= arr[i] <= 1000`
Could you solve this problem in O(n) time complexity?

### 解題

Runtime: 3 ms, faster than 59.29%
Memory Usage: 2.2 MB, less than 86.73%
func sumOddLengthSubarrays(arr []int) int {
sum := 0
for i:=1; i<=len(arr); i+=2 {
for j:=0; j<=len(arr)-i; j++ {
sum += sumup(arr[j:j+i])
}
}
return sum
}
func sumup(arr []int) int {
res := 0
for _, num := range arr {
res += num
}
return res
}