CODE

class Solution:
    def findUnsortedSubarray(self, nums: List[int]) -> int:
        # Find right limit of the subarray. Traverse array from left to right
        right_ptr = 0
        big = nums[0]
        for i in range(len(nums)):
            if nums[i] < big: 
                # a number smaller than what we have seen -> need sorting
                # This is the last index on the right that needs sorting 
                right_ptr = i
            else:
                big = nums[i]
        
        # Find left limit of the subarray. Traverse array from right to left
        left_ptr = 0
        small = nums[-1]
        for i in reversed(range(len(nums))):
            if nums[i] > small: 
                # a number bigger than what we have seen -> need sorting
                # This is the last index on the left that needs sorting 
                left_ptr = i
            else:
                small = nums[i]
                
        if right_ptr == left_ptr: return 0
        return right_ptr - left_ptr + 1