725. Split Linked List in Parts

Description

Given the head of a singly linked list and an integer k, split the linked list into k consecutive linked list parts.

The length of each part should be as equal as possible: no two parts should have a size differing by more than one. This may lead to some parts being null.

The parts should be in the order of occurrence in the input list, and parts occurring earlier should always have a size greater than or equal to parts occurring later.

Return an array of the k parts.

 

Example 1:

Input: head = [1,2,3], k = 5
Output: [[1],[2],[3],[],[]]
Explanation:
The first element output[0] has output[0].val = 1, output[0].next = null.
The last element output[4] is null, but its string representation as a ListNode is [].

Example 2:

Input: head = [1,2,3,4,5,6,7,8,9,10], k = 3
Output: [[1,2,3,4],[5,6,7],[8,9,10]]
Explanation:
The input has been split into consecutive parts with size difference at most 1, and earlier parts are a larger size than the later parts.

 

Constraints:

  • The number of nodes in the list is in the range [0, 1000].
  • 0 <= Node.val <= 1000
  • 1 <= k <= 50

Solutions

Solution 1

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


class Solution:
    def splitListToParts(self, root: ListNode, k: int) -> List[ListNode]:
        n, cur = 0, root
        while cur:
            n += 1
            cur = cur.next
        cur = root
        width, remainder = divmod(n, k)
        res = [None for _ in range(k)]
        for i in range(k):
            head = cur
            for j in range(width + (i < remainder) - 1):
                if cur:
                    cur = cur.next
            if cur:
                cur.next, cur = None, cur.next
            res[i] = head
        return res

Java Code
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/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode[] splitListToParts(ListNode root, int k) {
        int n = 0;
        ListNode cur = root;
        while (cur != null) {
            ++n;
            cur = cur.next;
        }
        // width 表示每一部分至少含有的结点个数
        // remainder 表示前 remainder 部分，每一部分多出一个数
        int width = n / k, remainder = n % k;
        ListNode[] res = new ListNode[k];
        cur = root;
        for (int i = 0; i < k; ++i) {
            ListNode head = cur;
            for (int j = 0; j < width + ((i < remainder) ? 1 : 0) - 1; ++j) {
                if (cur != null) {
                    cur = cur.next;
                }
            }
            if (cur != null) {
                ListNode t = cur.next;
                cur.next = null;
                cur = t;
            }
            res[i] = head;
        }
        return res;
    }
}