本文共 1885 字，大约阅读时间需要 6 分钟。

struct ListNode {	int val;	ListNode *next;	ListNode(int x) : val(x), next(NULL) {}};class Solution {public:	ListNode *partition(ListNode *head, int x) {		// Start typing your C/C++ solution below		// DO NOT write int main() function		ListNode* p = head;		ListNode* smallerNow = NULL;		ListNode* smallerHead = NULL;		ListNode* greaterNow = NULL;		ListNode* greaterHead = NULL;		while (p)		{			if(p->val < x)			{				if(!smallerHead) smallerNow = smallerHead = p;				else smallerNow->next = p, smallerNow = p;			}			else			{				if(!greaterHead) greaterNow = greaterHead = p;				else  greaterNow->next = p, greaterNow = p;			}			p = p->next;		}		if(greaterHead) greaterNow->next = NULL;		if(smallerHead) smallerNow->next = NULL;		if(!smallerHead && !greaterHead) return NULL;		else if(!smallerHead) return greaterHead;		else		{			smallerNow->next = greaterHead;			return smallerHead;		}	}};

second time

/** * 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) {        // Start typing your C/C++ solution below        // DO NOT write int main() function        ListNode dummy1(-1);        ListNode dummy2(-1);        ListNode* prev1 = &dummy1;        ListNode* prev2 = &dummy2;        ListNode* cur = head;        while(cur != NULL)        {            if(cur->val < x)            {                prev1->next = cur;                prev1 = prev1->next;            }            else            {                prev2->next = cur;                prev2 = prev2->next;            }            cur = cur->next;        }        prev1->next = NULL;        prev2->next = NULL;        if(dummy1.next == NULL) return dummy2.next;        else        {            prev1->next = dummy2.next;            return dummy1.next;        }    }};

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