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Program to arrange linked list nodes based on the value k in Python
Suppose we have a singly linked list and another value k. We have to arrange the nodes so that all nodes whose values are less than k come first, and all nodes whose values are equal to k next, and finally other nodes at last. The constraint is that the relative ordering of the nodes should remain the same.
So, if the input is like L = [4, 3, 6, 6, 6, 10, 8] k = 6, then the output will be [4, 3, 6, 6, 6, 10, 8, ]
To solve this, we will follow these steps −
- less_head := create a linked list node with value same as 0
- less := less_head
- equal_head := create a linked list node with value same as 0
- equal := equal_head
- greater_head := create a linked list node with value same as 0
- greater := greater_head
- cur := node
- while cur is not null, do
- if value of cur < k, then
- next of less := create a linked list node with value same as value of cur
- less := next of less
- otherwise when value of cur > k, then
- next of greater := create a linked list node with value same as value of cur
- greater := next of greater
- otherwise,
- next of equal := create a linked list node with value same as value of cur
- equal := next of equal
- cur := next of cur
- if value of cur < k, then
- next of less := next of equal_head
- next of equal := next of greater_head
- return next of less_head
Let us see the following implementation to get better understanding −
Example
class ListNode:
def __init__(self, data, next = None):
self.val = data
self.next = next
def make_list(elements):
head = ListNode(elements[0])
for element in elements[1:]:
ptr = head
while ptr.next:
ptr = ptr.next
ptr.next = ListNode(element)
return head
def print_list(head):
ptr = head
print('[', end = "")
while ptr:
print(ptr.val, end = ", ")
ptr = ptr.next
print(']')
class Solution:
def solve(self, node, k):
less_head = less = ListNode(0)
equal_head = equal = ListNode(0)
greater_head = greater = ListNode(0)
cur = node
while cur:
if cur.val < k:
less.next = ListNode(cur.val)
less = less.next
elif cur.val > k:
greater.next = ListNode(cur.val)
greater = greater.next
else:
equal.next = ListNode(cur.val)
equal = equal.next
cur = cur.next
less.next = equal_head.next
equal.next = greater_head.next
return less_head.next
ob = Solution()
L = make_list([4, 3, 6, 6, 6, 10, 8])
k = 6
print_list(ob.solve(L, k))Input
[4, 3, 6, 6, 6, 10, 8], 6
Output
[4, 3, 6, 6, 6, 10, 8, ]
Updated on: 19-Nov-2020
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