leetcode-143 重排链表

143. 重排链表

难度: 中等

---

/**
 * Definition for singly-linked list.
 * type ListNode struct {
 *     Val int
 *     Next *ListNode
 * }
 */
func reorderList(head *ListNode)  {
	if head == nil || head.Next == nil {
		return 
	}

	// 寻找中间结点
	p1 := head
	p2 := head
	for p2.Next != nil && p2.Next.Next != nil {
		p1 = p1.Next
		p2 = p2.Next.Next
	}

	// 反转链表后半部分  1->2->3->4->5->6 to 1->2->3->6->5->4
	preMiddle := p1
	preCurrent := p1.Next
	for preCurrent.Next != nil {
		current := preCurrent.Next
		preCurrent.Next = current.Next
		current.Next = preMiddle.Next
		preMiddle.Next = current
	}

	// 重新拼接链表  1->2->3->6->5->4 to 1->6->2->5->3->4
	p1 = head
	p2 = preMiddle.Next
	for p1 != preMiddle {
		preMiddle.Next = p2.Next
		p2.Next = p1.Next
		p1.Next = p2
		p1 = p2.Next
		p2 = preMiddle.Next
	}
	return 
}

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原文链接: https://dashen.tech/2015/03/01/leetcode-143-重排链表/

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