LeetCode-in-Java
1588. Sum of All Odd Length Subarrays
Easy
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 <= 1001 <= arr[i] <= 1000
Solution
public class Solution {
public int sumOddLengthSubarrays(int[] arr) {
int len = arr.length;
int sum = 0;
for (int i = 0; i <= len - 1; i++) {
sum = sum + (((i + 1) * (len - i) + 1) / 2) * arr[i];
}
return sum;
}
}