和为奇数的子数组数目

/*
题目思路：
利用Java Stream的方式来计算和为奇数的子数组数目。思路类似于普通的Java解法，通过计算前缀和的奇偶性来判断子数组的和是否为奇数。
*/

import java.util.stream.IntStream;

public class OddSumSubarraysStream {
    public static int countOddSumSubarrays(int[] arr) {
        final int MOD = 1000000007;
        int oddCount = 0, evenCount = 1, result = 0, prefixSum = 0;
        for (int num : arr) {
            prefixSum += num;
            if (prefixSum % 2 == 0) {
                result = (result + oddCount) % MOD;
                evenCount++;
            } else {
                result = (result + evenCount) % MOD;
                oddCount++;
            }
        }
        return result;
    }

    public static void main(String[] args) {
        int[] arr = {1, 3, 5};
        System.out.println(countOddSumSubarrays(arr)); // 输出：4
    }
}