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reverse_k.py
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reverse_k.py
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import json
# Definition for singly-linked list.
class ListNode(object):
def __init__(self, x):
self.val = x
self.next = None
# def linkListToString(head):
# p = head
# st = str(head.val)
# p = p.next
# while p is not None:
# st = st + '->' + str(p.val)
# p = p.next
# return st
class Solution(object):
def reverse_link(self, group_prev, group_tail):
group_head = group_prev.next
succ = group_tail.next
p = group_prev
q = p.next # CURRENT Pointer, init by group head
while q is not None and q != succ:
r = q.next
q.next = p
p = q
q = r
group_prev.next = group_tail
group_head.next = succ
group_tail = group_head
return group_prev, group_tail
def reverseKGroup(self, head, k):
"""
:type head: ListNode
:type k: int
:rtype: ListNode
"""
if head is None:
return head
lead = ListNode(0)
lead.next = head
group_prev = lead
group_head = group_prev.next
pointer = group_head
counter = 1
while pointer is not None:
if counter == k:
# change head-tail
group_prev, new_pointer = self.reverse_link(group_prev, pointer)
# start next journey
group_prev = new_pointer
group_head = group_prev.next
pointer = group_head
counter = 1
else:
pointer = pointer.next
counter += 1
return lead.next
def stringToListNode(input):
# Generate list from the input
numbers = json.loads(input)
# Now convert that list into linked list
dummyRoot = ListNode(0)
ptr = dummyRoot
for number in numbers:
ptr.next = ListNode(number)
ptr = ptr.next
ptr = dummyRoot.next
return ptr
def stringToInt(input):
return int(input)
def listNodeToString(node):
if not node:
return "[]"
result = ""
while node:
result += str(node.val) + ", "
node = node.next
return "[" + result[:-2] + "]"
def main():
import sys
def readlines():
for line in sys.stdin:
yield line.strip('\n')
lines = readlines()
while True:
try:
line = lines.next()
head = stringToListNode(line)
line = lines.next()
k = stringToInt(line)
ret = Solution().reverseKGroup(head, k)
out = listNodeToString(ret)
print out
except StopIteration:
break
if __name__ == '__main__':
main()