Number of subarrays with bounded maximum

Time: O(N); Space: O(1); medium

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 1:

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].

Notes:

  • L, R and A[i] will be an integer in the range [0, 10^9].

  • The length of A will be in the range of [1, 50000].

[1]:

class Solution1(object):
    def numSubarrayBoundedMax(self, A, L, R):
        """
        :type A: List[int]
        :type L: int
        :type R: int
        :rtype: int
        """
        def count(A, bound):
            result, curr = 0, 0
            for i in A :
                curr = curr + 1 if i <= bound else 0
                result += curr
            return result

        return count(A, R) - count(A, L-1)

[2]:

s = Solution1()
A = [2, 1, 4, 3]
L = 2
R = 3
assert s.numSubarrayBoundedMax(A, L, R) == 3