0713. Subarray Product Less Than K (M)

Subarray Product Less Than K (M)

題目

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 = 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.

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題意

找到全部的連續子數組，使其積小於指定值。

思路

遍歷數組全部元素做爲區間右端點；對於每一個右端點，找到最左側的元素，使構成的區間的積小於指定值；累加以右端點爲終點的子區間的數量。

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代碼實現

Java

public int numSubarrayProductLessThanK(int[] nums, int k) {
        int count = 0;
        int left = 0, product = 1;
        for (int right = 0; right < nums.length; right++) {
            product *= nums[right];
            while (product >= k && left <= right) {
                product /= nums[left++];
            }
            count += right - left + 1;
        }
        return count;
    }