Subarray Product Less than K

• Lintcode : 1075 / Leetcode : 713
• Level : Medium

Problem

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
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 = [5,10,2], k = 10
    Output:  2

    Explanation:
    Only [5] and [2].
Notice
0 < nums.length <= 50000.
0 < nums[i] < 1000.
0 <= k < 10^6.

Concept & Algorithm

筆記

Time Complexity & Space Complexity

time : O(n)
space: O(1)

Answer

class Solution {
public:
    int numSubarrayProductLessThanK(vector<int> &nums, int k) {
        int n = nums.size();
        if (k <= 1 || n == 0) return 0;
        int count = 0, left = 0, product = 1;
        for (int i = 0;i < n; i++) {
            product = product * nums[i];
            while (product >= k)
                product /= nums[left++];
            count += i - left + 1;
        }
        return count;
    }
};

tags: 2pointers

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