def reverseKGroup(self, head: ListNode, k: int) -> ListNode:
# 洗数据
if not head:
return head
dummy = ListNode(-1)
dummy.next = head
cur = dummy
while cur:
start = cur.next
# 将 start, end 置于 k 个节点的开头和末尾
end = cur
for _ in range(k):
end = end.next
if not end:
return dummy.next
nxt = end.next
# 将翻转后
start, end = self.reversList(start, end)
cur.next = start
end.next = nxt
# 进入下一轮
cur = end
return dummy.next
def reverseBetween(self, head: ListNode, m: int, n: int) -> ListNode:
dummy = ListNode(-1)
dummy.next = head
slow = fast = dummy
for _ in range(n):
fast = fast.next
for _ in range(m):
slow = slow.next
# 反转链表模板
prev = fast.next
cur = slow
while prev != fast:
nxt = cur.next
cur.next = prev
prev = cur
cur = nxt
# 现在 prev 是反转后，链表的头节点
# 需要将反转之后的链表，接回原链表
cur = dummy
for _ in range(m - 1):
cur = cur.next
cur.next = prev
return dummy.next
def test_insertion_sort_list(self):
s = Solution()
ListNode()
self.assertEqual(
'1->2->3->4',
s.insertionSortList(build_list('4->2->1->3')).entire_list())
self.assertEqual(
'-1->0->3->4->5',
s.insertionSortList(build_list('-1->5->3->4->0')).entire_list())
def test_delete_duplicates(self):
s = Solution()
ListNode()
self.assertEqual(
'1->2',
s.deleteDuplicates(build_list('1->1->2')).entire_list())
self.assertEqual(
'1->2->3',
s.deleteDuplicates(build_list('1->1->2->3->3')).entire_list())
def partition_dummy(self, head: ListNode, x: int) -> ListNode:
if not head:
return head
lth = ltt = ListNode()
geh = get = ListNode()
while head:
if head.val < x:
ltt.next = head
ltt = ltt.next
elif head.val >= x:
get.next = head
get = get.next
head = head.next
get.next = None
ltt.next = geh.next
return lth.next
def oddEvenList(self, head: ListNode) -> ListNode:
if not head:
return head
count = 1
eh = et = ListNode()
oh = ot = ListNode()
while head:
if count % 2 == 0:
et.next = head
et = et.next
else:
ot.next = head
ot = ot.next
head = head.next
count += 1
et.next = None
ot.next = eh.next
return oh.next
def get_left_mid(self, head) -> ListNode:
# 不接受空节点和单节点
if not head or not head.next:
raise ValueError('list must have at least two element')
dummy = ListNode(-1)
dummy.next = head
slow = dummy
fast = head
while fast and fast.next:
slow, fast = slow.next, fast.next.next
return slow
def removeNthFromEnd(self, head: ListNode, n: int) -> ListNode:
dummy = ListNode(-1)
dummy.next = head
fast = dummy
# 找到倒数 n + 1 的节点
for _ in range(n + 1):
# n 一定有效，所以这里无需判空
fast = fast.next
slow = dummy
while fast:
slow, fast = slow.next, fast.next
slow.next = slow.next.next
return dummy.next
def swapPairs(self, head: ListNode) -> ListNode:
# 洗数据
if not head or not head.next:
return head
dummy = ListNode(-1)
dummy.next = head
cur = dummy
while cur.next and cur.next.next:
first = cur.next
sec = cur.next.next
cur.next = sec
first.next = sec.next
sec.next = first
cur = cur.next.next
return dummy.next
def deleteNode(self, head: ListNode, val: int) -> ListNode:
# 洗数据
if not head:
return head
# 哑节点，方便删除头节点的情况
# 最后结果返回 dummy.next
dummy = ListNode(-1)
dummy.next = head
prev = dummy
cur = head
while cur:
if cur.val == val:
prev.next = prev.next.next
break
prev, cur = prev.next, cur.next
return dummy.next
def deleteDuplicates(self, head: ListNode) -> ListNode:
# 洗数据
if not head or not head.next:
return head
# 可能有头节点变动的情况，要哑节点
dummy = ListNode(-1)
dummy.next = head
cur = dummy
while cur and cur.next and cur.next.next:
if cur.next.val == cur.next.next.val:
end = cur.next.next
while end and end.val == cur.next.val:
end = end.next
cur.next = end
else:
cur = cur.next
return dummy.next
def mergeTwoLists(self, l1: ListNode, l2: ListNode) -> ListNode:
# 洗数据
if not l1 or not l2:
return l1 or l2
dummy = ListNode(-1)
cur = dummy
while l1 and l2:
if l1.val <= l2.val:
cur.next = l1
l1 = l1.next
else:
cur.next = l2
l2 = l2.next
cur = cur.next
cur.next = l1 or l2
return dummy.next
def insertionSortList(self, head: ListNode) -> ListNode:
if not head or not head.next:
return head
dummy = ListNode(-1)
prev = dummy
cur = head
while cur:
# 第一次进行插入排序，或者下一个节点应该插在前面
if not prev.next or prev.next.val >= cur.val:
prev = dummy
# <= 为了稳定排序，用 3->3->3 里例子看一下
while prev.next and prev.next.val <= cur.val:
prev = prev.next
# 找到插入位置，插入新节点
cur.next, prev.next, cur = prev.next, cur, cur.next
# 将 prev 放到开头
# prev = dummy
return dummy.next
def test_swap_pairs(self):
s = Solution()
ListNode()
self.assertEqual('2->1->4->3',
s.swapPairs(build_list("1->2->3->4")).entire_list())
def test_entire_list(self):
node = ListNode(1, ListNode(2, ListNode(3)))
self.assertEqual("1->2->3", entire_list(node))