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725. Split Linked List in Parts 👍

  • Time: $O(n)$
  • Space: $O(1)$
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class Solution {
 public:
  vector<ListNode*> splitListToParts(ListNode* root, int k) {
    vector<ListNode*> ans(k);
    const int length = getLength(root);
    const int subLength = length / k;
    int remainder = length % k;

    ListNode* prev = nullptr;
    ListNode* head = root;

    for (int i = 0; i < k; ++i, --remainder) {
      ans[i] = head;
      for (int j = 0; j < subLength + (remainder > 0); ++j) {
        prev = head;
        head = head->next;
      }
      if (prev != nullptr)
        prev->next = nullptr;
    }

    return ans;
  }

 private:
  int getLength(ListNode* root) {
    int length = 0;
    for (ListNode* curr = root; curr; curr = curr->next)
      ++length;
    return length;
  }
};

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class Solution {
  public ListNode[] splitListToParts(ListNode root, int k) {
    ListNode[] ans = new ListNode[k];
    final int length = getLength(root);
    final int subLength = length / k;
    int remainder = length % k;

    ListNode prev = null;
    ListNode head = root;

    for (int i = 0; i < k; ++i, --remainder) {
      ans[i] = head;
      for (int j = 0; j < subLength + (remainder > 0 ? 1 : 0); ++j) {
        prev = head;
        head = head.next;
      }
      if (prev != null)
        prev.next = null;
    }

    return ans;
  }

  private int getLength(ListNode root) {
    int length = 0;
    for (ListNode curr = root; curr != null; curr = curr.next)
      ++length;
    return length;
  }
}

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class Solution:
  def splitListToParts(self, root: ListNode, k: int) -> list[ListNode]:
    ans = [[] for _ in range(k)]
    length = 0
    curr = root
    while curr:
      length += 1
      curr = curr.next
    subLength = length // k
    remainder = length % k

    prev = None
    head = root

    for i in range(k):
      ans[i] = head
      for j in range(subLength + (1 if remainder > 0 else 0)):
        prev = head
        head = head.next
      if prev:
        prev.next = None
      remainder -= 1

    return ans