LeetCode 86. Partition List

Given 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.

For example,
Given 1->4->3->2->5->2 and x = 3,
return 1->2->2->4->3->5.

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/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* partition(ListNode *head, int x) {
        ListNode smaller_head(0);
        ListNode larger_head(0);
        ListNode *smaller_tail = &smaller_head;
        ListNode *larger_tail = &larger_head;
        while (head != NULL) {
            if (head->val < x) {
                smaller_tail->next = head;
                smaller_tail = head;
            }
            else {
                larger_tail->next = head;
                larger_tail = head;
            }
            head = head->next;
        }
        smaller_tail->next = larger_head.next;
        larger_tail->next = NULL;
        return smaller_head.next;
    }
};