1524. Number of Sub-arrays With Odd Sum

public class Solution
{
    public int NumOfSubarrays(int[] arr)
    {
        const int kMod = 1_000_000_007;
        int n = arr.Length;
        long ans = 0;

        // dp0[i] := the number of subarrays that end in arr[i - 1] with an even sum
        int[] dp0 = new int[n + 1];
        // dp1[i] := the number of subarrays that end in arr[i - 1] with an odd sum
        int[] dp1 = new int[n + 1];

        for (int i = 1; i <= n; ++i)
        {
            if (arr[i - 1] % 2 == 1)
            {
                dp0[i] = dp1[i - 1];
                dp1[i] = dp0[i - 1] + 1;
            }
            else
            {
                dp0[i] = dp0[i - 1] + 1;
                dp1[i] = dp1[i - 1];
            }
            ans = (ans + dp1[i]) % kMod;
        }

        return (int)ans;
    }
}