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

# Given an integer array, you need to find one continuous subarray that
# if you only sort this subarray in ascending order,
# then the whole array will be sorted in ascending order, too.
#
# You need to find the shortest such subarray and output its length.
#
# Example 1:
# Input: [2, 6, 4, 8, 10, 9, 15]
# Output: 5
# Explanation: You need to sort [6, 4, 8, 10, 9] in ascending order
# to make the whole array sorted in ascending order.
#
# Note:
# Then length of the input array is in range [1, 10,000].
# The input array may contain duplicates, so ascending order here means <=.

class Solution(object):
    def findUnsortedSubarray(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        n = len(nums)
        left, right = -1, -2
        min_from_right, max_from_left = nums[-1], nums[0]
        for i in xrange(1, n):
            max_from_left = max(max_from_left, nums[i])
            min_from_right = min(min_from_right, nums[n-1-i])
            if nums[i] < max_from_left: right = i
            if nums[n-1-i] > min_from_right: left = n-1-i
        return right - left + 1

Create shortest-unsorted-continuous-subarray.py