Linked lists memory view -...
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Linked lists memory view lst = Linked_list("abc") name space memory space lst next value next “a” value next “b” value next “c” None type: Node type: Node type: Node type: linked_list
Transcript of Linked lists memory view -...
Linked lists memory view
lst = Linked_list("abc")
name space
memory space
lst
next
value
next
“a”
value
next
“b”
value
next
“c”
None
type: Node type: Node type: Node type:
linked_list
next
next
lst.reverse()
value
next
“a”
value
next
“b”
value
next
“c”
None
value
next
“a”
value
next
“b”
value
next
“c”
None
Exercise: implement list reverse with O(1) additional memory
Guidance
value
next
value
next
value
next
1. Think about “the middle” of the process.
You have 2 consecutive elements prev, curr.
All elements up to prev were reversed.
Write the loop’s body.
2. Think about the initialization of prev, curr
3. Think about termination of the loop and
extra actions after it
value
next
prev curr
next
Solution
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next
“a”
value
next
“b”
value
next
“c”
None
def reverse(self):
prev = None
curr = self.next
while curr !=None:
tmp = curr.next
curr.next = prev
prev = curr
curr = tmp
self.next = prev
>>> lst = Linked_list("abcde")
>>> lst
[a,36067440] [b,36067376] [c,36067024] [d,36067312] [e,36066864]
>>> lst.reverse()
>>> lst
[e,36066864] [d,36067312] [c,36067024] [b,36067376] [a,36067440]
Demo
next
value
next
“a”
value
next
“b”
value
next
“c”
None
prev curr
Initialization
def reverse(self):
prev = None
curr = self.next
while curr !=None:
tmp = curr.next
curr.next = prev
prev = curr
curr = tmp
self.next = prev
None
Demo
next
value
next
“a”
value
next
“b”
value
next
“c”
None
prev curr
Step 1
def reverse(self):
prev = None
curr = self.next
while curr !=None:
tmp = curr.next
curr.next = prev
prev = curr
curr = tmp
self.next = prev
None
tmp
Demo
next
value
next
“a”
value
next
“b”
value
next
“c”
None
prev curr
Step 1
def reverse(self):
prev = None
curr = self.next
while curr !=None:
tmp = curr.next
curr.next = prev
prev = curr
curr = tmp
self.next = prev
None
tmp
Demo
next
value
next
“a”
value
next
“b”
value
next
“c”
None
prev curr
Step 1
def reverse(self):
prev = None
curr = self.next
while curr !=None:
tmp = curr.next
curr.next = prev
prev = curr
curr = tmp
self.next = prev
None
tmp
Demo
next
value
next
“a”
value
next
“b”
value
next
“c”
None
prev curr
Step 1
def reverse(self):
prev = None
curr = self.next
while curr !=None:
tmp = curr.next
curr.next = prev
prev = curr
curr = tmp
self.next = prev
None
tmp
Demo
next
value
next
“a”
value
next
“b”
value
next
“c”
None
prev curr
Step 2
def reverse(self):
prev = None
curr = self.next
while curr !=None:
tmp = curr.next
curr.next = prev
prev = curr
curr = tmp
self.next = prev
None
tmp
Demo
next
value
next
“a”
value
next
“b”
value
next
“c”
None
prev curr
Step 3
def reverse(self):
prev = None
curr = self.next
while curr !=None:
tmp = curr.next
curr.next = prev
prev = curr
curr = tmp
self.next = prev
None
tmp
Demo
next
value
next
“a”
value
next
“b”
value
next
“c”
None
prev curr
Termination
def reverse(self):
prev = None
curr = self.next
while curr !=None:
tmp = curr.next
curr.next = prev
prev = curr
curr = tmp
self.next = prev
None
tmp
