24. 两两交换链表中的节点

题目描述：

解题代码：

class Solution(object):
    def swapPairs(self, head):
        dummy_head = ListNode(next=head)
        cur = dummy_head
        while cur.next != None and cur.next.next != None:
            temp = cur.next
            temp1 = cur.next.next.next
            cur.next = cur.next.next
            cur.next.next = temp
            temp.next = temp1
            cur = cur.next.next
        return dummy_head.next

19.删除链表的倒数第N个节点

题目描述：

class Solution(object):
    def removeNthfromEnd(self, head, n):
        dummy_head = ListNode(next=head)
        fast = dummy_head
        slow = dummy_head
        for _ in range(n):
            fast = fast.next
        fast = fast.next
        while fast != None:
            fast = fast.next
            slow = slow.next
        slow.next = slow.next.next
        return dummy_head.next

面试题 02.07. 链表相交

题目描述：

解题代码：

class Solution(object):
    def getIntersectionNode(self, headA, headB):
        A, B = headA, headB
        while A != B:
            A = A.next if A else headB
            B = B.next if B else headA
        return A

环形链表

题目描述：

解题代码：

class Solution(object):
    def detectCycle(self, head):
        fast = head
        slow = head
        while fast != None and fast.next != None:
            fast = fast.next.next
            slow = slow.next
            if fast == slow:
                index1 = fast
                index2 = head
                while index1 != index2:
                    index1 = index1.next
                    index2 = index2.next
                return index2
        return None