# (prefix product + siliding win)713. Subarray Product Less Than K

T: O(n)

S: O(1)

````java
```java
class Solution {
    public int numSubarrayProductLessThanK(int[] nums, int k) {
        int n = nums.length;
        int left = 0;
        int right = 0;
        int product = 1;
        int result = 0;
        while (right < n) {
            product *= nums[right];
            right++;
            while (left < right && product >= k) {
                product /= nums[left];
                left++;
            }
            result += (right - left);
        }
        return result;
    }
}

/**
T: O(n)
S: O(1)

prefix product idea
and sliding win

10, 5,  2, 6 (origin)
10 50 100 600 (product)
    r         
l                 

1    r - l = 1   ([10])

10, 5,  2, 6 (origin)
10 50 100 600
        r
l
   2   r - l = 2  ([5], [10,5])

10, 5,  2, 6 (origin)
10 50 100  600
            r
   l         
      r - l = 2  ([2], [5,2])

10, 5,  2, 6 (origin)
10 50 100  600
   l            r
   r - l = 4 - 1 = 3 ([6], [2,6], [5,2,6])

   1 + 2 + 2 + 3 = 8  
 */
```
````
