[LeetCode]#1588. Sum of All Odd Length Subarrays

Environment: Python 3.8

Key technique: while

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

Analysis:

1. Calculate all possible pairs as below.
2. Return summary

Solution:

class Solution:
    def sumOddLengthSubarrays(self, arr):
        ans = 0
        for i in range(len(arr)):
            j = i + 1
            while j <= len(arr):
                ans += sum(arr[i:j])
                j += 2
        return ans

Submissions:

Reference:

https://leetcode.com/problems/sum-of-all-odd-length-subarrays/discuss/980723/Python-Non-Brute-Force-solution