def merge(self, l1: ListNode, l2: ListNode):
if not l1:
return l2
if not l2:
return l1
if l1.val < l2.val:
l1.next = self.merge(l1.next, l2)
return l1
l2.next = self.merge(l1, l2.next)
return l2
def isPalindrome(self, head: ListNode) -> bool:
lenh = 0
p = head
# 链表长度
while p:
lenh += 1
p = p.next
# 后半部分
mid = (lenh + 1) // 2
left, rightp = head, head
for _ in range(mid):
rightp = rightp.next
# 后半部分翻转
dumpy = ListNode(0)
while rightp:
tmp = rightp.next
rightp.next = dumpy.next
dumpy.next = rightp
rightp = tmp
right = dumpy.next
#回文判断
while right:
if left.val != right.val:
return False
left = left.next
right = right.next
return True
def reverseList(self, head: ListNode) -> ListNode:
dumpy = ListNode(0)
while head:
tmp = head
head = head.next
tmp.next = dumpy.next
dumpy.next = tmp
return dumpy.next
def reverseList(self, head: ListNode) -> ListNode:
dumpy = ListNode(0)
first = head
while head:
head = head.next
first.next = dumpy.next
dumpy.next = first
first = head
return dumpy.next
def reverseList(self, head: ListNode) -> ListNode:
res = ListNode(0)
p = head
while head:
head = head.next
p.next = res.next
res.next = p
p = head
return res.next
def deleteNode(self, head: ListNode, val: int) -> ListNode:
dumpy = ListNode(0)
dumpy.next = head
p = dumpy
while p.next:
if p.next.val == val:
p.next = p.next.next
break
p = p.next
return dumpy.next
def removeNthFromEnd(self, head: ListNode, n: int) -> ListNode:
dumpy = ListNode(0)
dumpy.next = head
p = dumpy
for _ in range(n):
head = head.next
while head:
head = head.next
p = p.next
p.next = p.next.next
return dumpy.next
def removeElements(self, head: ListNode, val: int) -> ListNode:
# 哨兵结点
dumpy = ListNode(0)
dumpy.next = head
prev, curr = dumpy, head
while curr:
if curr.val == val:
prev.next = curr.next
else:
prev = curr
curr = curr.next
return dumpy.next
def rotateRight(self, head: ListNode, k: int) -> ListNode:
if not head:
return head
p1 = head
lenh = 0
while p1.next:
p1 = p1.next
lenh += 1
lenh += 1
k %= lenh
if k == 0:
return head
dumpy = ListNode(0)
dumpy.next = head
p2 = head
for _ in range(lenh - k - 1):
p2 = p2.next
dumpy.next = p2.next
p1.next = head
p2.next = None
return dumpy.next
def removeNthFromEnd(head,n): dummy = ListNode(0) dummy.next = head fast = dummy while n: fast = fast.next n -= 1 listprint(fast) slow = dummy while fast.next: fast = fast.next slow = slow.next slow.next = slow.next.next return dummy.next
def deleteDuplicates(self, head: ListNode) -> ListNode:
if not head:
return head
dumpy = ListNode(0)
dumpy.next = head
p1, p2 = head, head
while p2.next:
if p2.next.val == p1.val:
p2 = p2.next
continue
p2 = p2.next
p1.next = p2
p1 = p2
p1.next = p2.next
return dumpy.next
def mergeTwoLists(self, l1: ListNode, l2: ListNode) -> ListNode:
dumpy = ListNode(0)
dumpy.next = l1
p = dumpy
while l1 and l2:
if l1.val <= l2.val:
l1 = l1.next
p = p.next
else:
p.next = l2
p = p.next
l2 = l2.next
p.next = l1
if l2:
p.next = l2
return dumpy.next
def addTwoNumbers(self, l1: ListNode, l2: ListNode) -> ListNode:
dumpy = ListNode(0)
dumpy.next = l1
l = dumpy
ans = 0
while l1 or l2:
a = l1.val if l1 else 0
b = l2.val if l2 else 0
ans += a + b
ans, mod = divmod(ans, 10)
l.next = ListNode(mod)
l = l.next
if l1:
l1 = l1.next
if l2:
l2 = l2.next
if ans > 0:
l.next = ListNode(1)
return dumpy.next
def swapPairs(head): if not head or not head.next: return head dummynode = ListNode(0) dummynode.next = head pre = dummynode first = head second = head.next while first and second: pre.next = second nex = second.next second.next = first first.next = nex pre = first if first.next: second = first.next.next first = first.next else: break return dummynode.next
def deleteDuplicates(self, head: ListNode) -> ListNode:
if not head:
return head
dumpy = ListNode(0)
dumpy.next = head
p1, p2, p3 = dumpy, head, head
count = 0
while p3.next:
if p3.next.val == p2.val:
p3 = p3.next
count += 1
continue
p3 = p3.next
p2 = p3
if count > 0:
p1.next = p3
else:
p1 = p1.next
count = 0
if count > 0:
p1.next = p3.next
return dumpy.next
n -= 1
listprint(fast)
slow = dummy
while fast.next:
fast = fast.next
slow = slow.next
slow.next = slow.next.next
return dummy.next
e1 = ListNode(1)
e2 = ListNode(2)
e3 = ListNode(3)
e4 = ListNode(4)
e5 = ListNode(5)
e6 = ListNode(6)
e7 = ListNode(7)
head = e1
e1.next = e2
e2.next = e3
e3.next = e4
e4.next = e5
e5.next = e6
e6.next = e7
listprint(head)
print('-----')
listprint(removeNthFromEnd(head,7))