LeetCode: Insert into a Cyclic Sorted List

Posted on July 28, 2018July 26, 2020 by braindenny

Insert into a Cyclic Sorted List

Similar Problems:

Given a node from a cyclic linked list which is sorted in ascending order, write a function to insert a value into the list such that it remains a cyclic sorted list. The given node can be a reference to any single node in the list, and may not be necessarily the smallest value in the cyclic list.

If there are multiple suitable places for insertion, you may choose any place to insert the new value. After the insertion, the cyclic list should remain sorted.

If the list is empty (i.e., given node is null), you should create a new single cyclic list and return the reference to that single node. Otherwise, you should return the original given node.

The following example may help you understand the problem better:

In the figure above, there is a cyclic sorted list of three elements. You are given a reference to the node with value 3, and we need to insert 2 into the list.

The new node should insert between node 1 and node 3. After the insertion, the list should look like this, and we should still return node 3.

Github: code.dennyzhang.com

Credits To: leetcode.com

Leave me comments, if you have better ways to solve.

Solution:

## https://code.dennyzhang.com/insert-into-a-cyclic-sorted-list
## Basic Ideas:
##    Find the smallest value which is no less than the target
##    If there are multiple suitable places for insertion, 
##      here we choose to insert into the first suitable place after head.
##
## Question: how we know we are running the loop again?
##
## Complexity: Time O(n), Space O(1)
"""
# Definition for a Node.
class Node:
    def __init__(self, val, next):
        self.val = val
        self.next = next
"""
class Solution:
    def insert(self, head, insertVal):
        """
        :type head: Node
        :type insertVal: int
        :rtype: Node
        """
        node = Node(insertVal, None)
        # empty
        if head is None:
            node.next = node
            return node

        # one node
        if head.next is None:
            head.next = node
            node.next = head
            return head

        # find the smallest value, which is no less than the target
        p = head
        while True:
            # end of the loop
            if p.val > p.next.val:
                # biggest or smallest
                if insertVal >= p.val or insertVal <= p.next.val:
                    break

                # should keep going
                if insertVal > p.next.val and insertVal < p.val:
                    p = p.next
                    continue
                break

            if insertVal >= p.val and insertVal <= p.next.val:
                break
            p = p.next
            if p == head:
                # run into the loop again
                break

        node.next = p.next
        p.next = node
        return head

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