[LeetCode] Challenge log 147

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147. Insertion Sort List

Algorithm: Insertion sort

Trick: If a node is greater than the sorted tail, make it the new tail and move on to next.

Sort a linked list using insertion sort.

img
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:

  1. Insertion sort iterates, consuming one input element each repetition, and growing a sorted output list.
  2. 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.
  3. It repeats until no input elements remain.

Example 1:

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Input: 4->2->1->3
Output: 1->2->3->4

Example 2:

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Input: -1->5->3->4->0
Output: -1->0->3->4->5
Soulution:
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class Solution:
    def insertionSortList(self, head):
        """
        :type head: ListNode
        :rtype: ListNode
        """
        if not head: return None
        
        newhead = ListNode(0)
        newhead.next = head
        sort = head
        cur = head.next
        while cur:
            # quick check if cur > sort
            if cur.val > sort.val:
                sort = cur
                cur = cur.next
                continue
            
            # delete cur
            nxt = cur.next
            sort.next = nxt 
            
            # insert cur
            pos = newhead
            while pos != sort and cur.val > pos.next.val:
                pos = pos.next    
            temp = pos.next
            pos.next = cur
            cur.next = temp
            
            # update cur
            cur = nxt
            
        return newhead.next
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