795. Number of Subarrays with Bounded Maximum

题目

We are given an array A of positive integers, and two positive integers L and R (L <= R).

Return the number of (contiguous, non-empty) subarrays such that the value of the maximum array element in that subarray is at least L and at most R.

Example :
Input:
A = [2, 1, 4, 3]
L = 2
R = 3
Output: 3
Explanation: There are three subarrays that meet the requirements: [2], [2, 1], [3].

Note:

1. L, R ; and A[i] will be an integer in the range [0, 10^9].
2. The length of A will be in the range of [1, 50000].

解题思路

见程序注释