README.md

1588. Sum of All Odd Length Subarrays

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

Solutions (Rust)

1. Solution

impl Solution {
    pub fn sum_odd_length_subarrays(arr: Vec<i32>) -> i32 {
        let mut d = (arr.len() as i32 + 1) / 2;
        let mut prev = d;
        let mut ret = 0;

        for i in 0..(arr.len() / 2) {
            let j = arr.len() - 1 - i;

            ret += (arr[i] + arr[j]) * prev;
            d -= match arr.len() % 2 {
                0 => 1,
                _ => 2 * (1 - i as i32 % 2),
            };
            prev += d;
        }

        if arr.len() % 2 == 1 {
            ret += arr[arr.len() / 2] * prev;
        }

        ret
    }
}