[Leetcode] 24. Swap Nodes in Pairs

　　在家瘫了半个月，虚弱时长2月半，又来水题了~

　　内存感人，不过想不出来不用temp保存中间值的链表交换方法了。

　　

Success

Details 

Runtime: 40 ms, faster than 44.76% of Python3 online submissions for Swap Nodes in Pairs.

Memory Usage: 13.6 MB, less than 6.06% of Python3 online submissions for Swap Nodes in Pairs.

 

Submission Detail

55 / 55 test cases passed.	Status:  Accepted
Runtime: 40 ms Memory Usage: 13.6 MB	Submitted: 2 minutes ago

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution:
    def swapPairs(self, head: ListNode) -> ListNode:
        # 0
        if head == None:
            return head
        # 1
        if head.next == None:
            return head
        # change head
        tempHead = head
        head = head.next
        tempHead.next = head.next
        head.next = tempHead
        #change Node after head
        currentprev = head.next
        current = head.next.next
        while True:
            if current != None and current.next != None:
                #do swap
                tempNext = current.next #node 4
                current.next = current.next.next #node 3 point to 5
                tempNext.next = current #node 4 point to 3
                currentprev.next = tempNext#node 1 point to 4

                #++1
                if current.next !=None:
                    currentprev = current
                    current = currentprev.next
                else:
                    break
            else:
                break
        return head

大佬的20ms：

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution:
    def swapPairs(self, head):
        dummy = p = ListNode(0)
        dummy.next = head
        while head and head.next:
            tmp = head.next
            head.next = tmp.next
            tmp.next = head
            p.next = tmp
            head = head.next
            p = tmp.next
        return dummy.next

 不过这个也是用的temp做交换啊 只是循环简单一点。。。怎么就只有20ms了