学步园

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 tox.

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) {}
 * };
 */
#define LN ListNode
class Solution {
public:
    ListNode *partition(ListNode *head, int x) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        
        LN sguard(-1);
	    LN hguard(-1);
	    LN* sTail=&sguard;
	    LN* hTail=&hguard;
	    while(head)
	    {
		    if (head->val<x)
		    {
			    sTail->next=head;
			    sTail=head;
		    }
		    else
		    {
			    hTail->next=head;
			    hTail=head;
		    }
		    head=head->next;
	    }
	    sTail->next=hguard.next;
	    hTail->next=NULL;
	    return sguard.next;
    }
};