SubarrayProductLessThanK.java

package two_pointers; /**
 * Created by gouthamvidyapradhan on 17/02/2018.
 * Your are given an array of positive integers nums.

 Count and print the number of (contiguous) subarrays where the product of all the elements in the subarray is 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.
 Note:

 0 < nums.length <= 50000.
 0 < nums[i] < 1000.
 0 <= k < 10^6.
 */

import java.util.ArrayDeque;
import java.util.Queue;

public class SubarrayProductLessThanK {

    public static void main(String[] args) throws Exception{
        int[] A = {10,2,2,5,4,4,4,3,7,7};
        System.out.println(new SubarrayProductLessThanK().numSubarrayProductLessThanK(A, 289));
    }


    public int numSubarrayProductLessThanK(int[] nums, int k) {
        long prod = 1;
        int count = 0;
        Queue<Integer> queue = new ArrayDeque<>();
        for(int i = 0; i < nums.length; i++){
            if(nums[i] < k){
                count++;
                if((prod * nums[i]) < k){
                    prod *= nums[i];
                    if(!queue.isEmpty()){
                        count += (i - queue.peek());
                    }
                }else{
                    while(!queue.isEmpty()){
                        int last = queue.poll();
                        prod /= nums[last];
                        if((prod * nums[i]) < k){
                            prod = prod * nums[i];
                            if(!queue.isEmpty()){
                                count += (i - queue.peek());
                            }
                            break;
                        }
                    }
                }
                if(queue.isEmpty()){
                    prod = nums[i];
                }
                queue.offer(i);
            } else{
                queue.clear();
            }
        }
        return count;
    }

}