【leetcode】147. Insertion Sort List

题目如下：

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:

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:

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

Example 2:

Input: -1->5->3->4->0
Output: -1->0->3->4->5

解题思路：题目不难，每个节点找到对应的位置插入即可。

代码如下：

# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution(object):
    def insertionSortList(self, head):
        """
        :type head: ListNode
        :rtype: ListNode
        """
        newHead = None
        while head != None:
            if newHead == None:
                newHead = ListNode(head.val)
                head = head.next
                continue
            node = newHead
            new_node = ListNode(head.val)

            #insert as the head
            if node.val > head.val:
                new_node.next = newHead
                newHead = new_node
                head = head.next
                continue
            while node != None:
                if node.next != None and node.val <= head.val and node.next.val >= head.val:
                    new_node.next = node.next
                    node.next = new_node
                    break
                elif node.next == None:
                    node.next = new_node
                    break
                node = node.next
            head = head.next
        return newHead