713. Subarray Product Less Than K

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题目

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 = 100Output: 8Explanation: 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.

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思路

本题思路比较巧妙，维护两个索引j和i，每次统计当乘积小于k时j-i的数量。

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代码

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