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:
1 <= arr.length <= 1051 <= arr[i] <= 100
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);
}
}