147.InsertionSortList.go

/*
147. Insertion Sort List
Medium

Given the head of a singly linked list, sort the list using insertion sort, and return the sorted list's head.

The steps of the insertion sort algorithm:

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.
The following is a graphical example of the insertion sort algorithm. The partially sorted list (black) initially contains only the first element in the list. One element (red) is removed from the input data and inserted in-place into the sorted list with each iteration.


 

Example 1:


Input: head = [4,2,1,3]
Output: [1,2,3,4]
Example 2:


Input: head = [-1,5,3,4,0]
Output: [-1,0,3,4,5]
 

Constraints:

The number of nodes in the list is in the range [1, 5000].
-5000 <= Node.val <= 5000
*/
/**
 * Definition for singly-linked list.
 * type ListNode struct {
 *     Val int
 *     Next *ListNode
 * }
 */
 func insertionSortList(head *ListNode) *ListNode {
    var dummy ListNode
    var prev, curr, next *ListNode
    prev = &dummy
    curr = head
    
    for curr != nil {
        next = curr.Next
        for prev.Next != nil && prev.Next.Val < curr.Val { prev = prev.Next}
        
        curr.Next = prev.Next
        prev.Next = curr
        
        prev = &dummy
        curr = next
    }
    
    return dummy.Next
}