14. Partition List.cpp

/*
Partition List
==============

Given the head of a linked list and a value x, partition it such that all nodes less than x come before nodes greater than or equal to x.

You should preserve the original relative order of the nodes in each of the two partitions.

Example 1:
Input: head = [1,4,3,2,5,2], x = 3
Output: [1,2,2,4,3,5]

Example 2:
Input: head = [2,1], x = 2
Output: [1,2]

Constraints:
The number of nodes in the list is in the range [0, 200].
-100 <= Node.val <= 100
-200 <= x <= 200
*/

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */

class Solution
{
public:
  void partition(vector<int> &arr, int x)
  {
  }

  ListNode *partition(ListNode *head, int x)
  {
    ListNode *newHead = new ListNode(-1);
    auto temp = head, newTemp = newHead;

    while (temp)
    {
      if (temp->val < x)
      {
        ListNode *newNode = new ListNode(temp->val);
        newTemp->next = newNode;
        newTemp = newTemp->next;
      }
      temp = temp->next;
    }

    temp = head;
    while (temp)
    {
      if (temp->val >= x)
      {
        ListNode *newNode = new ListNode(temp->val);
        newTemp->next = newNode;
        newTemp = newTemp->next;
      }
      temp = temp->next;
    }

    return newHead->next;
  }
};