Given an integer array nums, return the number of subarrays filled with 0. A subarray is a contiguous non-empty sequence of elements within an array.

zeroFilledSubarray.js

/**
 * @param {number[]} nums
 * @return {number}
 */
var zeroFilledSubarray = function(nums) {
    let total = 0;      // Final count of zero-filled subarrays
    let count = 0;      // Tracks length of current zero streak

    for (let i = 0; i < nums.length; i++) {
        if (nums[i] === 0) {
            // Extend the current zero streak
            count++;
        } else if (count > 0) {
            // End of a zero streak: add subarray count using arithmetic sum formula
            total += (count * (count + 1)) / 2;
            count = 0; // Reset for next streak
        }
        // If nums[i] !== 0 and count === 0, just continue
    }

    // Handle case where array ends with zeros
    if (count > 0) {
        total += (count * (count + 1)) / 2;
    }

    return total;
};