#143

Reorder List

medium· Linked Listruns: 0

You are given the head of a singly linked list L0 -> L1 -> ... -> Ln-1 -> Ln. Reorder the list to be of the form L0 -> Ln -> L1 -> Ln-1 -> L2 -> Ln-2 -> .... You may not modify the values in the list's nodes; only the nodes themselves may be changed.

wpm 0acc 100%time 0:000 / 691

class Solution:
    def reorderList(self, head: ListNode | None) -> None:
        if not head or not head.next:
            return
        slow, fast = head, head.next
        while fast and fast.next:
            slow = slow.next
            fast = fast.next.next
        second = slow.next
        slow.next = None
        prev = None
        while second:
            nxt = second.next
            second.next = prev
            prev = second
            second = nxt
        first, second = head, prev
        while second:
            tmp1, tmp2 = first.next, second.next
            first.next = second
            second.next = tmp1
            first = tmp1
            second = tmp2

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