Sort a linked list using insertion sort.
A graphical example of insertion sort. The partial sorted list (black) initially contains only the first element in the list. With each iteration one element (red) is removed from the input data and inserted in-place into the sorted list
Algorithm of Insertion Sort:
Insertion sort iterates, consuming one input element each repetition, and growing a sorted output list. At each iteration, insertion sort removes one element from the input data, finds the location it belongs within the sorted list, and inserts it there. It repeats until no input elements remain.
Example 1:
Input: 4->2->1->3
Output: 1->2->3->4
Example 2:
Input: -1->5->3->4->0
Output: -1->0->3->4->5
- What made this more difficult is that this is a linked list.
- Follow the insertion sort algorithm: have a empty linked list and add items to it in sorted order by comparing it to elements in the list.
# Definition for singly-linked list.
# class ListNode:
# def __init__(self, val=0, next=None):
# self.val = val
# self.next = next
class Solution:
def insertionSortList(self, head: ListNode) -> ListNode:
result = None
ptr = head
def insertSort(head, node):
ptr = head
back = None
inserted = False
while ptr:
if ptr.val < node.val:
back = ptr
ptr = ptr.next
continue
else:
node.next = ptr
if back:
back.next = node
else:
head = node
inserted = True
break
if not inserted:
back.next = node
return head
while ptr:
node = ptr
ptr = ptr.next
node.next = None
if result is None:
result = node
else:
result = insertSort(result, node)
return result