Judgment of monotonic series

An array is monotonic if it is monotonically increasing or monotonically  decreasing .

Example 1:

Input: nums = [1,2,2,3]
Output: true

Example 2:

Input: nums = [6,5,4,4]
Output: true

Example 3:

input: nums = [1,3,2]
output: false

Source: LeetCode
Link: https://leetcode.cn/problems/monotonic-array
 

class Solution(object):
    def isMonotonic(self, nums):
        """
        :type nums: List[int]
        :rtype: bool
        """
        b=[]
        j=1
        for i in range(len(nums)):
            if j>=len(nums):
                break
            if nums[i]==nums[j]:
                j+=1
                continue
            c=nums[i]-nums[j]
            j+=1
            b.append(c)
        if all(i>0 for i in b) or all(i<0 for i in b) :
            return True
        else:
            return False