def mergeTwoLists(self, l1: ListNode, l2: ListNode) -> ListNode:
if not l1:
return l2
if not l2:
return l1
if l1.val < l2.val:
l1.next = self.mergeTwoLists(l1.next, l2)
return l1
else:
l2.next = self.mergeTwoLists(l1, l2.next)
return l2
def reverseList1(self, head):
"""
:type head: ListNode
:rtype: ListNode
"""
# 迭代：头插法
dummy = ListNode(0)
while head:
q = head.next
head.next = dummy.next
dummy.next = head
head = q
return dummy.next
def removeElements2(self, head, val):
"""
:type head: ListNode
:type val: int
:rtype: ListNode
"""
# 大神简化版，思想同上
dummy = ListNode(0)
dummy.next = head
cur = dummy
while cur.next:
if cur.next.val == val:
cur.next = cur.next.next
else:
cur = cur.next
return dummy.next
def swapPairs1(self, head):
"""
:type head: ListNode
:rtype: ListNode
"""
# 循环
dummy = ListNode(0)
dummy.next = head
current = dummy
while current.next and current.next.next:
node1 = current.next
node2 = node1.next
node1.next = node2.next
node2.next = node1
current.next = node2
current = current.next.next
return dummy.next
def removeElements1(self, head, val):
"""
:type head: ListNode
:type val: int
:rtype: ListNode
"""
# 遍历链表，使用哑节点，不需为头结点特殊定制逻辑
dummy = ListNode(0)
dummy.next = head
pre = dummy
p = head
while p:
if p.val == val:
pre.next = p.next
del p
p = pre.next
else:
pre = pre.next
p = p.next
return dummy.next
def addTwoNumbers(self, l1, l2):
"""
:type l1: ListNode
:type l2: ListNode
:rtype: ListNode
"""
dummy = ListNode(0)
dummy.next = l2
cur = dummy
carry = 0
while l1 or l2:
x = l1.val if l1 else 0
y = l2.val if l2 else 0
sum = x + y + carry
carry = sum // 10
cur.next = ListNode(sum % 10)
cur = cur.next
l1 = l1.next if l1 else None
l2 = l2.next if l2 else None
if carry:
cur.next = ListNode(carry)
return dummy.next
# 递归
# 终止条件：当l1为空或l2为空时结束
# 返回值：每一层调用都返回排序好的链表头
# 本级递归内容：如果l1的val值更小，则将l1.next与排序好的链表头相接；l2同理
def mergeTwoLists(self, l1: ListNode, l2: ListNode) -> ListNode:
if not l1:
return l2
if not l2:
return l1
if l1.val < l2.val:
l1.next = self.mergeTwoLists(l1.next, l2)
return l1
else:
l2.next = self.mergeTwoLists(l1, l2.next)
return l2
if __name__ == '__main__':
l1 = ListNode(1)
l1.next = ListNode(2)
l1.next.next = ListNode(4)
l2 = ListNode(1)
l2.next = ListNode(3)
l2.next = ListNode(4)
Sol = Solution()
res = Sol.mergeTwoLists(l1, l2)
while res:
print(res.val)
res = res.next
cur = cur.next
return dummy.next
def removeElements3(self, head, val):
"""
:type head: ListNode
:type val: int
:rtype: ListNode
"""
# 递归
if not head:
return None
head.next = self.removeElements3(head.next, val)
if head.val == val:
return head.next
else:
return head
if __name__ == '__main__':
head = ListNode(1)
head.next = ListNode(2)
head.next.next = ListNode(3)
Sol = Solution()
res = Sol.removeElements3(head, val=3)
p = res
while p:
print(p.val)
p = p.next
dummy = ListNode(0)
dummy.next = l2
cur = dummy
carry = 0
while l1 or l2:
x = l1.val if l1 else 0
y = l2.val if l2 else 0
sum = x + y + carry
carry = sum // 10
cur.next = ListNode(sum % 10)
cur = cur.next
l1 = l1.next if l1 else None
l2 = l2.next if l2 else None
if carry:
cur.next = ListNode(carry)
return dummy.next
if __name__ == '__main__':
l1 = ListNode(5)
# l1.next = ListNode(4)
# l1.next.next = ListNode(3)
l2 = ListNode(5)
# l2.next = ListNode(6)
# l2.next.next = ListNode(4)
Sol = Solution()
res = Sol.addTwoNumbers(l1, l2)
print(res)
p = r
r = r.next
p.next = pre
return p
def reverseList3(self, head):
"""
:type head: ListNode
:rtype: ListNode
"""
# 递归
# 1.找终止条件。节点或下一个节点不存在时终止。
# 2.找返回值。返回翻转后的链表。
# 3.本级递归应该做什么。
if not head or not head.next:
return head
p = self.reverseList3(head.next)
head.next.next = head
head.next = None
return p
if __name__ == '__main__':
head = ListNode(1)
Sol = Solution()
res = Sol.reverseList3(head)
p = res
while p:
print(p.val)
p = p.next