You are given an array x of n positive numbers. You start at point (0,0) and moves x[0] metres to the north, then x[1] metres to the west,
    x[2] metres to the south,
    x[3] metres to the east and so on. In other words, after each move your direction changes
    counter-clockwise.
    Write a one-pass algorithm with O(1) extra space to determine, if your path crosses itself, or not.
Example 1:
Given x = [2, 1, 1, 2],
?????
?   ?
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    ?
Return true (self crossing)
Example 2:
Given x = [1, 2, 3, 4],
????????
?      ?
?
?
?????????????>
Return false (not self crossing)
Example 3:
Given x = [1, 1, 1, 1],
?????
?   ?
?????>
Return true (self crossing)
Credits:Special thanks to @dietpepsi for adding this problem and creating all test cases.
class Solution:
     def isSelfCrossing(self, x):
         """
         :type x: List[int]
         :rtype: bool
         """
         n = len(x)
         if n < 4:
             return False
 
         i = 3
         while i < n:
             if x[i] >= x[i - 2] and x[i - 3] >= x[i - 1]:
                 return True
             if i >= 4:
                 if x[i - 1] == x[i - 3] and x[i] + x[i - 4] >= x[i - 2]:
                     return True
             if i >= 5:
                 if x[i] >= x[i - 2] - x[i - 4] >= 0 and x[i - 5] >= x[i - 3] - x[i - 1] >= 0:
                     return True
             i += 1
         return False

class Solution:
     def isSelfCrossing(self, x):
         """
         :type x: List[int]
         :rtype: bool
         """
         n = len(x)
         if n < 4:
             return False
 
         i = 3
         while i < n:
             if x[i] >= x[i - 2] and x[i - 3] >= x[i - 1]:
                 return True
             if i >= 4:
                 if x[i - 1] == x[i - 3] and x[i] + x[i - 4] >= x[i - 2]:
                     return True
             if i >= 5:
                 if x[i] >= x[i - 2] - x[i - 4] >= 0 and x[i - 5] >= x[i - 3] - x[i - 1] >= 0:
                     return True
             i += 1
         return False
