leetcode-148-排序链表*

题目描述：

方法一：快排

class Solution:
    def sortList(self, head: ListNode) -> ListNode:
        def partition(start, end): 
            node = start.next.next 
            pivotPrev = start.next 
            pivotPrev.next = end 
            pivotPost = pivotPrev 
            while node != end: 
                temp = node.next 
                if node.val > pivotPrev.val: 
                    node.next = pivotPost.next 
                    pivotPost.next = node 
                elif node.val < pivotPrev.val: 
                    node.next = start.next 
                    start.next = node 
                else: 
                    node.next = pivotPost.next 
                    pivotPost.next = node 
                    pivotPost = pivotPost.next 
                node = temp 
            return [pivotPrev, pivotPost] 
        def quicksort(start, end): 
            if start.next != end: 
                prev, post = partition(start, end) 
                quicksort(start, prev) 
                quicksort(post, end) 
        newHead = ListNode(0) 
        newHead.next = head 
        quicksort(newHead, None) 
        return newHead.next

方法二：归并排序

class Solution: 
    def sortList(self, head: ListNode) -> ListNode: 
        if not head or not head.next: return head 
        slow, fast = head, head.next 
        while fast and fast.next:
            fast, slow = fast.next.next, slow.next 
        mid, slow.next = slow.next, None 
        left, right = self.sortList(head), self.sortList(mid) 
        h = res = ListNode(0) 
        while left and right: 
            if left.val < right.val: 
                h.next, left = left, left.next 
            else: 
                h.next, right = right, right.next 
            h = h.next 
        h.next = left if left else right 
        return res.next