725. Split Linked List in Parts - Explanation

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def splitListToParts(self, head: Optional[ListNode], k: int) -> List[Optional[ListNode]]:
        arr, cur = [], head
        while cur:
            arr.append(cur)
            cur = cur.next

        N = len(arr)
        base_len, remainder = N // k, N % k

        res = [None] * k
        start = 0
        for i in range(k):
            if start < N:
                res[i] = arr[start]
                tail = start + base_len - 1
                if remainder:
                    tail += 1
                    remainder -= 1
                arr[tail].next = None
                start = tail + 1

        return res

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def splitListToParts(self, head: Optional[ListNode], k: int) -> List[Optional[ListNode]]:
        length, curr = 0, head
        while curr:
            curr = curr.next
            length += 1

        base_len, remainder = length // k, length % k
        curr, res = head, []

        for i in range(k):
            res.append(curr)
            for j in range(base_len - 1 + (1 if remainder else 0)):
                if not curr:
                    break
                curr = curr.next
            remainder -= 1 if remainder else 0
            if curr:
                curr.next, curr = None, curr.next

        return res