def reverseKGroup(self, head: ListNode, k: int) -> ListNode:
def reverse(node):
if not node.next:
return node
next = reverse(node.next)
next.next = node
return node
if k == 1:
return head
virtual_head = ListNode()
virtual_head.next = head
pre_head = virtual_head
head = virtual_head.next
while True:
# print(head.val)
if not head:
break
temp = head
temp_num = 1
while temp_num != k and temp.next:
temp = temp.next
temp_num += 1
if temp_num < k:
break
else:
# 记录尾部节点和after尾部节点
tail = temp
after_tail = temp.next
tail.next = None
reverse(head)
# 将逆转之后的头节点跟前一个节点链接 尾节点跟后一个链接
pre_head.next = tail
head.next = after_tail
# 记录新的头
pre_head = head
head = after_tail
return virtual_head.next
def mergeTwoLists(self, l1: ListNode, l2: ListNode) -> ListNode:
if not l1 and not l2:
return None
if not l2:
l1.next = self.mergeTwoLists(l1.next, l2)
return l1
if not l1:
l2.next = self.mergeTwoLists(l1, l2.next)
return l2
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 sortList(self, head: ListNode) -> ListNode:
if not head:
return None
# print('head = %d' % head.val)
if not head.next:
return head
# 获取长度
length = 0
index = head
while index:
index = index.next
length = length + 1
mid = int(length / 2)
# print('length = %d' % length)
# 获取中间节点
index = head
mid_index = 0
while index:
mid_index = mid_index + 1
if mid_index == mid:
break
index = index.next
# print('mid_index = %d' % index.val)
# 截断变成两节
right = index.next
index.next = None
# 将左右分别排序
left = self.sortList(head)
right = self.sortList(right)
# print('left = %d, left.next is %s, right = %d, right.next is %s' % (left.val, left.next, right.val, right.next))
# 合并
temp = ListNode(0)
current = temp
while left or right:
# print('current = %d, left is %s, right is %s' % (current.val, left, right))
if left and right:
if left.val < right.val:
current.next = left
left = left.next
else:
current.next = right
right = right.next
else:
if not left:
current.next = right
right = right.next
else:
current.next = left
left = left.next
current = current.next
return temp.next
def partition(self, head: ListNode, x: int) -> ListNode:
min_head = ListNode(0)
max_head = ListNode(0)
min_tail = min_head
max_tail = max_head
index = head
while index:
if index.val >= x:
max_tail.next = ListNode(index.val)
max_tail = max_tail.next
else:
min_tail.next = ListNode(index.val)
min_tail = min_tail.next
index = index.next
min_tail.next = max_head.next
return min_head.next
def removeNthFromEnd(self, head: ListNode, n: int) -> ListNode:
if not head.next:
return None
num = 0
vir_head = ListNode(0)
vir_head.next = head
temp = vir_head
real_temp = vir_head
while temp.next:
num += 1
temp = temp.next
if num > n:
real_temp = real_temp.next
if real_temp.next == head:
return head.next
else:
real_temp.next = real_temp.next.next
return head
def reorderList(self, head: ListNode) -> None:
"""
Do not return anything, modify head in-place instead.
"""
# 获取长度
length = 0
index = head
while index:
index = index.next
length = length + 1
mid = int(length / 2)
# print('length = %d' % length)
# 获取中间节点
index = head
mid_index = 0
while index:
mid_index = mid_index + 1
if mid_index == mid:
break
index = index.next
# print('mid_index = %d' % index.val)
# 截断变成两节
right = index.next
index.next = None
# 反转后节
current = None
next = right
while next:
next_next = next.next
next.next = current
current = next
next = next_next
# 合共两节
new_head = ListNode(0)
index = new_head
while current or head:
if head:
index.next = head
index = index.next
head = head.next
if current:
index.next = current
index = index.next
current = current.next
print('ok')
if left and right:
if left.val < right.val:
current.next = left
left = left.next
else:
current.next = right
right = right.next
else:
if not left:
current.next = right
right = right.next
else:
current.next = left
left = left.next
current = current.next
return temp.next
if __name__ == '__main__':
solution = Solution()
one = ListNode(4)
two = ListNode(2)
thr = ListNode(1)
fou = ListNode(3)
one.next = two
two.next = thr
thr.next = fou
print(solution.sortList(one))
def mergeKLists(self, lists: List[ListNode]) -> ListNode:
if not lists:
return None
def push(val, node):
heap.append((val, node))
pos = len(heap) - 1
while pos > 0:
father = (pos - 1) >> 1
parent_val, parent_node = heap[father]
if parent_val > val:
heap[pos] = (parent_val, parent_node)
pos = father
continue
break
heap[pos] = (val, node)
def pop():
last_val, last_node = heap.pop()
if heap:
return_val, return_node = heap[0]
pos = 0
child = 2 * pos + 1
while child < len(heap):
right_child = child + 1
if right_child < len(
heap) and heap[right_child][0] < heap[child][0]:
child = right_child
if heap[child][0] < last_val:
heap[pos] = heap[child]
pos = child
child = 2 * pos + 1
else:
break
heap[pos] = (last_val, last_node)
return (return_val, return_node)
return (last_val, last_node)
heap = []
for node in lists:
if node:
push(node.val, node)
head = ListNode()
temp = head
while heap:
val, node = pop()
if node.next:
push(node.next.val, node.next)
temp.next = node
temp = temp.next
return head.next
def detectCycle(self, head: ListNode) -> ListNode:
if not head:
return None
found = set()
while head:
found.add(head)
# print(head.val)
# print(found)
if head.next and head.next in found:
return head.next
head = head.next
return None
if __name__ == '__main__':
solution = Solution()
one = ListNode(1)
two = ListNode(2)
thr = ListNode(3)
fou = ListNode(4)
one.next = two
two.next = thr
thr.next = fou
fou.next = two
print(solution.detectCycle(one))
if not head:
return
tempHead = head
li = []
while tempHead:
li.append(tempHead)
tempHead = tempHead.next
x, y = 0, len(li) - 1
while x < y:
li[x].next = li[y]
x += 1
if x >= y:
break
li[y].next = li[x]
y -= 1
if x >= y:
li[x].next = None
if __name__ == '__main__':
# 测试用例
# 构建链表
newList = ListNode.create([1, 2, 3, 4, 5, 6, 7, 8, 9])
# 输出转换之前链表
print(ListNode.toList(newList))
# 进行转换
Solution().reorderList(newList)
# 输出转换之后列表
print(ListNode.toList(newList))
"""
反转链表
:param head: 头节点
:return:新头节点
"""
if head is None or head.next is None:
return
lastList = None
midList = head
nextList = midList.next
while midList.next is not None:
midList.next = lastList
lastList = midList
midList = nextList
nextList = midList.next
midList.next = lastList
return midList
if __name__ == "__main__":
# 测试用例
# 新建一个链表
newList = ListNode.create([0, 1, 2, 3, 4])
# 输出原先的链表
print(ListNode.toList(newList))
# 反转链表
newList = Solution().reverseList(newList)
# 输出新的链表
print(ListNode.toList(newList))
next.next = current
current = next
next = next_next
# 合共两节
new_head = ListNode(0)
index = new_head
while current or head:
if head:
index.next = head
index = index.next
head = head.next
if current:
index.next = current
index = index.next
current = current.next
print('ok')
if __name__ == '__main__':
solution = Solution()
one = ListNode(1)
# two = ListNode(2)
# thr = ListNode(3)
# fou = ListNode(4)
#
# one.next = two
# two.next = thr
# thr.next = fou
print(solution.reorderList(one))