feat(896-monotonic-array): better solution

0896_monotonic-array/python3/solution.py

@@ -1,16 +1,29 @@
 class Solution:
     def isMonotonic(self, nums: List[int]) -> bool:
-        direction = 0
-        prev = nums[0]
+        # Means difference between two nums indicate that it is
+        # decreasing or that difference is 0
+        isNonIncreasing = True
         
-        for num in nums[1:]:
-            newDirection = num - prev
+        # Same idea as above butnopposite: it is either increasing
+        # or difference is 0
+        isNonDecreasing = True
+        
+        for i in range(1, len(nums)):
+            difference = nums[i] - nums[i - 1]
             
-            if direction == 0:
-                direction = newDirection
-            elif direction < 0 < newDirection or direction > 0 > newDirection:
+            # We can say with confidence if this condition ever passes
+            # that sequence is increasing (e.g. 1 2 4 8 ...)
+            if difference > 0:
+                isNonIncreasing = False
+            # Sequence is decreasing (e.g. 1 0 -2 -4 ...)
+            elif difference < 0:
+                isNonDecreasing = False
+                
+            # If both flags are set to False, that means there is no
+            # monotonous state and we can break early.
+            if not isNonIncreasing and not isNonDecreasing:
                 return False
-            
-            prev = num
         
-        return True
+        # At the end, if either flag remains True, we have a montonous
+        # array
+        return isNonIncreasing or isNonDecreasing