update

[B]linked-list/[B]linked-list/25-reverse-nodes-in-k-group.py

@@ -6,46 +6,35 @@
 class Solution:
  def reverseKGroup(self, head: Optional[ListNode], k: int) -> Optional[ListNode]:
 
-
- def rev_group(prev_nodes, old_start, old_end, next_nodes):
-
+ def rev(prev_nodes, old_head, old_tail, next_nodes):
  prev = None
- cur = old_start
+ cur = old_head
  while cur and cur != next_nodes:
  nxt = cur.next
  cur.next = prev
  prev = cur
  cur = nxt
- new_start = prev
- new_end = old_start
- prev_nodes.next = new_start
- new_end.next = next_nodes
-
- return new_end, next_nodes
-
-
- dummy = ListNode()
- dummy.next = head
+ new_head = prev
+ prev_nodes.next = new_head
+ new_tail = old_head
+ new_tail.next = next_nodes
+ return new_tail
 
- prev = dummy
+ dummy = ListNode(next=head)
+ total = 0
+ prev_nodes = dummy
+ old_head = head
  cur = head
- prev_nodes = None
- old_start = None
- old_end = None
- next_nodes = None
- count = 0
  while cur:
- count += 1
- if count == 1:
- prev_nodes = prev
- old_start = cur
- if count == k:
- old_end = cur
- next_nodes = cur.next
- prev, cur = rev_group(prev_nodes, old_start, old_end, next_nodes)
- count = 0
- else:
- prev, cur = cur, cur.next
+ total += 1
+ if total == 1:
+ old_head = cur
+ if total == k:
+ new_tail = rev(prev_nodes, old_head, cur, cur.next)
+ prev_nodes = new_tail
+ cur = new_tail
+ total = 0
+ cur = cur.next
  return dummy.next
 
 # time O(n)

[B]linked-list/linked-list.md

@@ -113,21 +113,19 @@ prev and cur
  return prev
 
  # version 2
- def reverse_nodes(self, prev_nodes, old_start, old_end, next_nodes):
-
+ def reverse_nodes(prev_nodes, old_head, old_tail, next_nodes):
  prev = None
- cur = old_start
+ cur = old_head
  while cur and cur != next_nodes:
  nxt = cur.next
  cur.next = prev
  prev = cur
  cur = nxt
- new_start = prev
- new_end = old_start
- prev_nodes.next = new_start
- new_end.next = next_nodes
-
- return new_end, next_nodes
+ new_head = prev
+ prev_nodes.next = new_head
+ new_tail = old_head
+ new_tail.next = next_nodes
+ return new_tail
  ```
 
 - swap nodes in pairs

[K]graph/[K]graph-bfs/133-clone-graph.py

@@ -11,16 +11,23 @@ def __init__(self, val = 0, neighbors = None):
 class Solution:
  def cloneGraph(self, node: Optional['Node']) -> Optional['Node']:
  if not node:
- return None
- old_new = {node: Node(node.val)}
- queue = deque([node])
+ return node
+ old_new = {}
+ queue = deque([])
+ visited = set()
+ queue.append(node)
+ visited.add(node)
  while queue:
- old = queue.popleft()
- for old_neighbor in old.neighbors:
- if old_neighbor not in old_new:
- old_new[old_neighbor] = Node(old_neighbor.val)
- queue.append(old_neighbor)
- old_new[old].neighbors.append(old_new[old_neighbor])
+ old_node = queue.popleft()
+ if old_node not in old_new:
+ old_new[old_node] = Node(old_node.val)
+ for neighbor in old_node.neighbors:
+ if neighbor not in old_new:
+ old_new[neighbor] = Node(neighbor.val)
+ old_new[old_node].neighbors.append(old_new[neighbor])
+ if neighbor not in visited:
+ queue.append(neighbor)
+ visited.add(neighbor)
  return old_new[node]
 
 # time O(n)