725. 分隔链表

方法一：

class Solution(object):
    def splitListToParts(self, root, k):
        """
        :type root: ListNode
        :type k: int
        :rtype: List[ListNode]
        """
        # 题目说了，头结点是root，不是首节点
        cur = root
        # 统计原链表的长度
        length = 0
        while cur:
            length += 1
            cur = cur.next
        # 平均长度
        avelen = int(length / k)
        # 余数
        extra = length % k
        # 结果中应有extra个长为avalen+1的链表，k-extra个长为avalen的链表。
        nodeList = []

        """先截取extra个长度为avelen + 1的链表"""
        avelen += 1
        while extra > 0:
            # 每趟循环前记录头指针
            head = root
            pre = None
            for i in range(avelen):
                pre = root
                root = root.next
            pre.next = None
            nodeList.append(head)
            extra -= 1

        """再截取k-extra个长度为avelen的链表"""
        k = k - (length % k)
        avelen -= 1
        if avelen == 0:
            while k > 0:
                nodeList.append(None)
                k -= 1
        while k > 0:
            if root:
                head = root
                pre = None
                for i in range(avelen):
                    pre = root
                    root = root.next
                pre.next = None
                nodeList.append(head)
            else:
                nodeList.append(None)
            k -= 1
        return nodeList