# 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

```java
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.
*/
```