#1524 - Number of Sub-arrays With Odd Sum

Medium • View on LeetCode • View on GitHub

Problem 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.

Solution

/**
 * @param {number[]} arr
 * @return {number}
 */
var numOfSubarrays = function(arr) {
  let even = 0;
  let odd = 0;

  for (let i = 0, total = 0; i < arr.length; i++) {
    total += arr[i];
    odd += +(total % 2 === 1);
    even += +(total % 2 === 0);
  }

  return (odd * even + odd) % (1e9 + 7);
};