LeetCode-in-Java

1524. Number of Sub-arrays With Odd Sum

Medium

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

Constraints:

Solution

public class Solution {
    public int numOfSubarrays(int[] arr) {
        int number = arr[0] % 2 == 0 ? 0 : 1;
        long res = number;
        for (int i = 1; i < arr.length; i++) {
            if (arr[i] % 2 != 0) {
                number = i - number + 1;
            }
            res += number;
        }
        long mod = 1_000_000_007;
        return (int) (res % mod);
    }
}