2058. Find the Minimum and Maximum Number of Nodes Between Critical Points

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def nodesBetweenCriticalPoints(self, head: Optional[ListNode]) -> List[int]:
        def getNext(node):
            if node.next:
                return node.next.val
            return node.val

        lastStep = None
        minDist = float('inf')
        maxDist = -1
        firstStep = None

        def travel(node, prev, step):
            nonlocal minDist, maxDist, lastStep, firstStep

            if node:
                val = node.val
                nextVal = getNext(node)

                if (val > prev and val > nextVal) or (val < prev and val < nextVal):
                    if lastStep:
                        minDist = min(minDist, step - lastStep)
                        maxDist = max(maxDist, step - firstStep)    
                    else:
                        firstStep = step 

                    lastStep = step

                travel(node.next, node.val, step + 1)

        travel(head, head.val, 1)

        return [minDist if minDist != float('inf') else -1, maxDist]