number-of-subarrays-with-bounded-maximum.py

# Time:  O(n)
# Space: O(1)

# 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:
# - 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].

class Solution(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)