#1524
Number of Sub-arrays With Odd Sum
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array · math · dynamic programming · prefix sum
Description
Given an array of integers arr, return the number of subarrays with an odd sum.
Since the answer can be very large, return it modulo 109 + 7.
Example 1:
Input: arr = [1,3,5]
Output: 4
Explanation: All subarrays are [[1],[1,3],[1,3,5],[3],[3,5],[5]]
All sub-arrays sum are [1,4,9,3,8,5].
Odd sums are [1,9,3,5] so the answer is 4.
Example 2:
Input: arr = [2,4,6]
Output: 0
Explanation: All subarrays are [[2],[2,4],[2,4,6],[4],[4,6],[6]]
All sub-arrays sum are [2,6,12,4,10,6].
All sub-arrays have even sum and the answer is 0.
Example 3:
Input: arr = [1,2,3,4,5,6,7]
Output: 16
Solution