class Stack(object):
def __init__(self):
self.items = LinkedList()
def __str__(self):
s = ', '.join(map(str, self.items))
return 'Stack(>[' + s + '])'
def __len__(self):
return len(self.items)
def isEmpty(self):
return len(self) == 0
def push(self, item):
self.items.appendleft(item)
def pop(self):
try:
return self.items.popleft()
except KeyError:
return None
def peek(self):
return self.items[0]
def clear(self):
while not self.isEmpty():
self.pop()
def merge_linkedlists(alist: LinkedList, blist: LinkedList) -> LinkedList:
newlist = LinkedList()
p1, p2 = alist.head, blist.head
k1, k2 = 0, 0
while p1.next and p2.next:
v1, v2 = p1.next.data, p2.next.data
if v1 >= v2:
newlist.append(v1)
p1 = p1.next
k1 += 1
else:
newlist.append(v2)
p2 = p2.next
k2 += 1
if p1 is not None and p2 is None:
newlist.tail.next = p2
newlist.tail = blist.tail
newlist._size += len(blist) - k2
elif p1 is None and p2 is not None:
newlist.tail.next = p1
newlist.tail = alist.tail
newlist._size += len(alist) - k1
return newlist
def reverse_linkedlist(alist: LinkedList) -> LinkedList:
alist.tail = alist.head.next
p = None
while alist.head.next is not None:
tmp = alist.head.next
alist.head.next = tmp.next
tmp.next = p
p = tmp
alist.head.next = p
return alist
class Queue(object):
def __init__(self):
self.items = LinkedList()
def __str__(self):
s = ', '.join(map(str, self.items))
return f'Queue([{s}]<)'
def __len__(self):
return len(self.items)
def enqueue(self, item):
"""Items enqueue in the rear(tail) of the list"""
self.items.append(item)
def dequeue(self):
"""Items dequeue from the front(head) of the list"""
return self.items.popleft()
def isEmpty(self):
return len(self) == 0
"""
★ Task: To reverse a linkedlist ★
"""
from datastruct.collections import LinkedList
def reverse_linkedlist(alist: LinkedList) -> LinkedList:
alist.tail = alist.head.next
p = None
while alist.head.next is not None:
tmp = alist.head.next
alist.head.next = tmp.next
tmp.next = p
p = tmp
alist.head.next = p
return alist
if __name__ == '__main__':
l = LinkedList([0, 3, 2, 4])
print(reverse_linkedlist(l))
"""
★ Task: Find the middle node of a LinkedList ★
Idea: Set two pointers, the second pointer takes twice the steps as the first one does. When the second reaches
the end, the first points the middle node.
"""
from datastruct.collections import LinkedList
def middle_node(alist: LinkedList):
p1 = p2 = alist.head.next
while p2 is not None and p2.next is not None:
p1 = p1.next
p2 = p2.next.next
return p1.data
if __name__ == '__main__':
l = LinkedList([1, 2, 3, 4, 5, 6, 7, 8, 9])
print(middle_node(l))
while p1.next and p2.next:
v1, v2 = p1.next.data, p2.next.data
if v1 >= v2:
newlist.append(v1)
p1 = p1.next
k1 += 1
else:
newlist.append(v2)
p2 = p2.next
k2 += 1
if p1 is not None and p2 is None:
newlist.tail.next = p2
newlist.tail = blist.tail
newlist._size += len(blist) - k2
elif p1 is None and p2 is not None:
newlist.tail.next = p1
newlist.tail = alist.tail
newlist._size += len(alist) - k1
return newlist
if __name__ == '__main__':
a = LinkedList([6, 3, 1])
b = LinkedList([10, 9, 2, 0, -2])
c = merge_linkedlists(a, b)
print(c)
print(c[2:-1])
def __init__(self):
self.items = LinkedList()