[LeetCode] 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

.

/**
* 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) {
if(head == NULL)
return head;
ListNode *p = head;
ListNode *lessHead = NULL,*greaterHead =NULL,*pLess=NULL,*pGreater=NULL;
while(p){
if(p->val < x ){
if(lessHead == NULL){
lessHead = p;
pLess = p;
}else{
pLess->next = p;
pLess = pLess->next;
}
}else{
if(greaterHead == NULL){
greaterHead = p ;
pGreater  = p;
}else{
pGreater->next = p;
pGreater = pGreater->next;
}
}
p = p->next;
}//end while
if(pGreater!=NULL)
pGreater->next = NULL;
if(pLess !=NULL){
pLess->next = greaterHead;
return lessHead;
}else{
return greaterHead;
}

}//end func

};