0713. Subarray Product Less Than K

https://leetcode.com/problems/subarray-product-less-than-k

Description

Given an array of integers nums and an integer k, return the number of contiguous subarrays where the product of all the elements in the subarray is strictly less than k.

Example 1:

**Input:** nums = [10,5,2,6], k = 100
**Output:** 8
**Explanation:** The 8 subarrays that have product less than 100 are:
[10], [5], [2], [6], [10, 5], [5, 2], [2, 6], [5, 2, 6]
Note that [10, 5, 2] is not included as the product of 100 is not strictly less than k.

Example 2:

**Input:** nums = [1,2,3], k = 0
**Output:** 0

Constraints:

• 1 <= nums.length <= 3 * 104

• 1 <= nums[i] <= 1000

• 0 <= k <= 106

ac

class Solution {
    public int numSubarrayProductLessThanK(int[] nums, int k) {
        // edge cases
        if (nums == null || nums.length == 0 || k <= 1) return 0;

        int windowProduct = 1;
        int count = 0;

        for (int r = 0, l = 0; r < nums.length; r++) {
            windowProduct *= nums[r];

            while (windowProduct >= k) {
                windowProduct /= nums[l];
                l++;
            }

            count += r - l + 1;  // when a new element add to right, it forms window size new subarray
        }

        return count;
    }
}

/*
key: how to process the window
sliding window idea: when window formed, do something.
*/