leetcode 86. 分隔链表(Partition List)

题目描述：

给定一个链表和一个特定值 x，对链表进行分隔，使得所有小于 x 的节点都在大于或等于 x 的节点之前。

你应当保留两个分区中每个节点的初始相对位置。

示例:

输入: head = 1->4->3->2->5->2, x = 3
输出: 1->2->2->4->3->5

---

解法：

/**
 * 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* lhead = NULL, *lcur = NULL, *rhead = NULL, *rcur = NULL;
        ListNode* cur = head;
        while(cur != NULL){
            if(cur->val < x){
                if(lhead == NULL){
                    lhead = new ListNode(cur->val);
                    lcur = lhead;
                }else{
                    lcur->next = new ListNode(cur->val);
                    lcur = lcur->next;
                }
            }else{
                if(rhead == NULL){
                    rhead = new ListNode(cur->val);
                    rcur = rhead;
                }else{
                    rcur->next = new ListNode(cur->val);
                    rcur = rcur->next;
                }
            }
            cur = cur->next;
        }
        if(lhead == NULL){
            return rhead;
        }else{
            lcur->next = rhead;
            return lhead;
        }
    }
};